The Vietnam War was a conflict in Vietnam, Laos, and Cambodia from 1 November 1955 to the fall of Saigon on 30 April 1975. It was the second of the Indochina Wars and a major conflict of the Cold War. While the war was officially fought between North Vietnam and South Vietnam, the north was supported by the Soviet Union, China, and other countries in the Eastern Bloc, while the south was supported by the US and anti-communist allies. This made the conflict a proxy war between the US and Soviet Union. Direct US military involvement lasted from 1965 until its withdrawal in 1973. The fighting spilled over into the Laotian and Cambodian civil wars, which ended with all three countries becoming communist in 1975.

After the fall of French Indochina with the 1954 Geneva Conference, the country gained independence from France but was divided into two parts: the Viet Minh took control of North Vietnam, while the US assumed financial and military support for South Vietnam. The North Vietnamese controlled Viet Cong (VC), a South Vietnamese common front of militant leftists, socialists, communists, workers, peasants and intellectuals, initiated guerrilla war in the south. The People's Army of Vietnam (PAVN) engaged in more conventional warfare with US and Army of the Republic of Vietnam (ARVN) forces. North Vietnam invaded Laos in 1958, establishing the Ho Chi Minh trail to supply and reinforce the VC. By 1963, the north had sent 40,000 soldiers to fight in the south. US involvement increased under President John F. Kennedy, from 900 military advisors at the end of 1960 to 16,300 at the end of 1963.

Following the Gulf of Tonkin incident in 1964, the US Congress passed a resolution that gave President Lyndon B. Johnson authority to increase military presence, without a declaration of war. Johnson ordered deployment of combat units and dramatically increased American military personnel to 184,000 by the end of 1965, and to 536,000 by the end of 1968. US and South Vietnamese forces relied on air supremacy and overwhelming firepower to conduct search and destroy operations. The US conducted a strategic bombing campaign against North Vietnam and built up its forces, despite little progress. In 1968, North Vietnam launched the Tet Offensive; a tactical defeat, but a strategic victory, as it caused US domestic support to fade. In 1969, North Vietnam declared the Provisional Revolutionary Government of the Republic of South Vietnam. The 1970 deposing of Cambodia's monarch, resulted in a PAVN invasion of the country, and then a US-ARVN counter-invasion, escalating Cambodia's Civil War. After Richard Nixon's inauguration in 1969, a policy of "Vietnamization" began, which saw the conflict fought by an expanded ARVN, while US forces withdrew due to domestic opposition. US ground forces had mostly withdrawn by 1972, the 1973 Paris Peace Accords saw all US forces withdrawn and were broken almost immediately: fighting continued for two years. Phnom Penh fell to the Khmer Rouge in April 1975, while the 1975 spring offensive saw the Fall of Saigon to the PAVN, marking the end of the war. North and South Vietnam were reunified on 2 July the following year.

The war exacted enormous human cost: estimates of Vietnamese soldiers and civilians killed range from 970,000 to 3 million. Some 275,000–310,000 Cambodians, 20,000–62,000 Laotians, and 58,220 US service members died. Its end would precipitate the Vietnamese boat people and the larger Indochina refugee crisis, which saw millions leave Indochina, an estimated 250,000 perished at sea. The US destroyed 20% of South Vietnam's jungle and 20–50% of the mangrove forests, by spraying over 20 million U.S. gallons (75 million liters) of toxic herbicides; a notable example of ecocide. The Khmer Rouge carried out the Cambodian genocide, while conflict between them and the unified Vietnam escalated into the Cambodian–Vietnamese War. In response, China invaded Vietnam, with border conflicts lasting until 1991. Within the US, the war gave rise to Vietnam syndrome, a public aversion to American overseas military involvement, which, with the Watergate scandal, contributed to the crisis of confidence that affected America throughout the 1970s.

Various names have been applied and have shifted over time, though Vietnam War is the most commonly used title in English. It has been called the Second Indochina War since it spread to Laos and Cambodia, the Vietnam Conflict, and Nam (colloquially 'Nam). In Vietnam it is commonly known as Kháng chiến chống Mỹ (lit. 'Resistance War against America'). The Government of Vietnam officially refers to it as the Resistance War against America to Save the Nation. It is sometimes called the American War.

Vietnam had been under French control as part of French Indochina since the mid-19th century. Under French rule, Vietnamese nationalism was suppressed, so revolutionary groups conducted their activities abroad, particularly in France and China. One such nationalist, Nguyen Sinh Cung, established the Indochinese Communist Party in 1930, a Marxist–Leninist political organization which operated primarily in Hong Kong and the Soviet Union. The party aimed to overthrow French rule and establish an independent communist state in Vietnam.

In September 1940, Japan invaded French Indochina, following France's capitulation to Nazi Germany. French influence was suppressed by the Japanese, and in 1941 Cung, now known as Ho Chi Minh, returned to Vietnam to establish the Viet Minh, an anti-Japanese resistance movement that advocated for independence. The Viet Minh received aid from the Allies, namely the US, Soviet Union, and Republic of China. Beginning in 1944, the US Office of Strategic Services (O.S.S.) provided the Viet Minh with weapons, ammunition, and training to fight the occupying Japanese and Vichy French forces. Throughout the war, Vietnamese guerrilla resistance against the Japanese grew dramatically, and by the end of 1944 the Viet Minh had grown to over 500,000 members. US President Franklin D. Roosevelt was an ardent supporter of Vietnamese resistance, and proposed that Vietnam's independence be granted under an international trusteeship following the war.

Following the surrender of Japan in 1945, the Viet Minh launched the August Revolution, overthrowing the Japanese-backed Empire of Vietnam and seizing weapons from the surrendering Japanese forces. On September 2, Ho Chi Minh proclaimed the Declaration of independence of the Democratic Republic of Vietnam (DRV). However, on September 23, French forces overthrew the DRV and reinstated French rule. American support for the Viet Minh promptly ended, and O.S.S. forces left as the French sought to reassert control of the country.

Tensions between the Viet Minh and French authorities had erupted into full-scale war by 1946, a conflict which soon became entwined with the wider Cold War. On March 12, 1947, US President Harry S. Truman announced the Truman Doctrine, an anticommunist foreign policy which pledged US support to nations resisting "attempted subjugation by armed minorities or by outside pressures". In Indochina, this doctrine was first put into practice in February 1950, when the United States recognized the French-backed State of Vietnam in Saigon, led by former Emperor Bảo Đại, as the legitimate government of Vietnam, after the communist states of the Soviet Union and People's Republic of China recognized the Democratic Republic of Vietnam, led by Ho Chi Minh, as the legitimate Vietnamese government the previous month. The outbreak of the Korean War in June convinced Washington policymakers that the war in Indochina was another example of communist expansionism, directed by the Soviet Union.

Military advisors from China began assisting the Viet Minh in July 1950. Chinese weapons, expertise, and laborers transformed the Viet Minh from a guerrilla force into a regular army. In September 1950, the US further enforced the Truman Doctrine by creating a Military Assistance and Advisory Group (MAAG) to screen French requests for aid, advise on strategy, and train Vietnamese soldiers. By 1954, the US had spent $1 billion in support of the French military effort, shouldering 80% of the cost of the war.

During the Battle of Dien Bien Phu in 1954, US carriers sailed to the Gulf of Tonkin and the US conducted reconnaissance flights. France and the US discussed the use of tactical nuclear weapons, though reports of how seriously this was considered and by whom, are vague. According to then-Vice President Richard Nixon, the Joint Chiefs of Staff drew up plans to use nuclear weapons to support the French. Nixon, a so-called "hawk", suggested the US might have to "put American boys in". President Dwight D. Eisenhower made American participation contingent on British support, but the British were opposed. Eisenhower, wary of involving the US in an Asian land war, decided against intervention. Throughout the conflict, US intelligence estimates remained skeptical of France's chance of success.

On 7 May 1954, the French garrison at Dien Bien Phu surrendered. The defeat marked the end of French military involvement in Indochina. At the Geneva Conference, they negotiated a ceasefire with the Viet Minh, and independence was granted to Cambodia, Laos, and Vietnam.

At the 1954 Geneva Conference, Vietnam was temporarily partitioned at the 17th parallel. Ho Chi Minh wished to continue war in the south, but was restrained by Chinese allies who convinced him he could win control by electoral means. Under the Geneva Accords, civilians were allowed to move freely between the two provisional states for a 300-day period. Elections throughout the country were to be held in 1956 to establish a unified government. However, the US, represented at the conference by Secretary of State John Foster Dulles, objected to the resolution; Dulles' objection was supported only by the representative of Bảo Đại. John Foster's brother, Allen Dulles, who was director of the Central Intelligence Agency, then initiated a psychological warfare campaign which exaggerated anti-Catholic sentiment among the Viet Minh and distributed propaganda attributed to Viet Minh threatening an American attack on Hanoi with atomic bombs.

During the 300-day period, up to one million northerners, mainly minority Catholics, moved south, fearing persecution by the Communists. The exodus was coordinated by a U.S.-funded $93 million relocation program, which involved the French Navy and the US Seventh Fleet to ferry refugees. The northern refugees gave the later Ngô Đình Diệm regime a strong anti-communist constituency. Over 100,000 Viet Minh fighters went to the north for "regroupment", expecting to return south within two years. The Viet Minh left roughly 5,000 to 10,000 cadres in the south as a base for future insurgency. The last French soldiers left South Vietnam in April 1956 and the PRC also completed its withdrawal from North Vietnam.

Between 1953 and 1956, the North Vietnamese government instituted agrarian reforms, including "rent reduction" and "land reform", which resulted in political oppression. During land reform, North Vietnamese witnesses suggested a ratio of one execution for every 160 village residents, which extrapolates to 100,000 executions. Because the campaign was mainly in the Red River Delta area, 50,000 executions became accepted by scholars. However, declassified documents from Vietnamese and Hungarian archives indicate executions were much lower, though likely greater than 13,500. In 1956, leaders in Hanoi admitted to "excesses" in implementing this program and restored much of the land to the original owners.

The south, meanwhile, constituted the State of Vietnam, with Bảo Đại as Emperor, and Ngô Đình Diệm as prime minister. Neither the US, nor Diệm's State of Vietnam, signed anything at the Geneva Conference. The non-communist Vietnamese delegation objected strenuously to any division of Vietnam, but lost when the French accepted the proposal of Viet Minh delegate Phạm Văn Đồng, who proposed Vietnam eventually be united by elections under the supervision of "local commissions". The US countered with what became known as the "American Plan", with the support of South Vietnam and the UK. It provided for unification elections under the supervision of the UN, but was rejected by the Soviet delegation. The US said, "With respect to the statement made by the representative of the State of Vietnam, the United States reiterates its traditional position that peoples are entitled to determine their own future and that it will not join in any arrangement which would hinder this". US President Eisenhower wrote in 1954:

I have never talked or corresponded with a person knowledgeable in Indochinese affairs who did not agree that had elections been held as of the time of the fighting, possibly 80% of the population would have voted for the Communist Ho Chi Minh as their leader rather than Chief of State Bảo Đại. Indeed, the lack of leadership and drive on the part of Bảo Đại was a factor in the feeling prevalent among Vietnamese that they had nothing to fight for.

According to the Pentagon Papers, which commented on Eisenhower's observation, Diệm would have been a more popular candidate than Bảo Đại against Hồ, stating that "It is almost certain that by 1956 the proportion which might have voted for Ho - in a free election against Diem - would have been much smaller than 80%." In 1957, independent observers from India, Poland, and Canada representing the International Control Commission (ICC) stated that fair elections were impossible, with the ICC reporting that neither South nor North Vietnam had honored the armistice agreement.

From April to June 1955, Diệm eliminated political opposition in the south by launching operations against religious groups: the Cao Đài and Hòa Hảo of Ba Cụt. The campaign also attacked the Bình Xuyên organized crime group, which was allied with members of the communist party secret police and had military elements. The group was defeated in April following a battle in Saigon. As broad-based opposition to his harsh tactics mounted, Diệm increasingly sought to blame the communists.

In a referendum on the future of the State of Vietnam in October 1955, Diệm rigged the poll supervised by his brother Ngô Đình Nhu and was credited with 98% of the vote, including 133% in Saigon. His American advisors had recommended a more "modest" winning margin of "60 to 70 percent." Diệm, however, viewed the election as a test of authority. He declared South Vietnam to be an independent state under the name Republic of Vietnam (ROV), with him as president. Likewise, Ho Chi Minh and other communists won at least 99% of the vote in North Vietnamese "elections".

The domino theory, which argued that if a country fell to communism, all surrounding countries would follow, was first proposed by the Eisenhower administration. John F. Kennedy, then a senator, said in a speech to the American Friends of Vietnam: "Burma, Thailand, India, Japan, the Philippines and obviously Laos and Cambodia are among those whose security would be threatened if the Red Tide of Communism overflowed into Vietnam."

A devout Roman Catholic, Diệm was fervently anti-communist, nationalist, and socially conservative. Historian Luu Doan Huynh notes "Diệm represented narrow and extremist nationalism coupled with autocracy and nepotism." Most Vietnamese were Buddhist, and alarmed by Diệm's actions, like his dedication of the country to the Virgin Mary.

In the summer of 1955, Diệm launched the "Denounce the Communists" campaign, during which suspected communists and other anti-government elements were arrested, imprisoned, tortured, or executed. He instituted the death penalty in August 1956 against activity deemed communist. The North Vietnamese government claimed that, by November 1957, over 65,000 individuals were imprisoned and 2,148 killed in the process. According to Gabriel Kolko, 40,000 political prisoners had been jailed by the end of 1958. In October 1956, Diệm launched a land reform program limiting the size of rice farms per owner. 1.8m acres of farm land became available for purchase by landless people. By 1960, the process had stalled because many of Diem's biggest supporters were large landowners.

In May 1957, Diệm undertook a 10-day state visit to the US. President Eisenhower pledged his continued support, and a parade was held in Diệm's honor. But Secretary of State Dulles privately conceded Diệm had to be backed because they could find no better alternative.

Between 1954 and 1957, the Diệm government succeeded in preventing large-scale organized unrest in the countryside. In April 1957, insurgents launched an assassination campaign, referred to as "extermination of traitors". 17 people were killed in the Châu Đốc massacre at a bar in July, and in September a district chief was killed with his family. By early 1959, Diệm had come to regard the violence as an organized campaign and implemented Law 10/59, which made political violence punishable by death and property confiscation. There had been division among former Viet Minh, whose main goal was to hold elections promised in the Geneva Accords, leading to "wildcat" activities separate from the other communists and anti-GVN activists. Douglas Pike estimated that insurgents carried out 2,000 abductions, and 1,700 assassinations of government officials, village chiefs, hospital workers and teachers from 1957 to 1960. Violence between insurgents and government forces increased drastically from 180 clashes in January 1960, to 545 clashes in September.

In September 1960, COSVN, North Vietnam's southern headquarters, ordered a coordinated uprising in South Vietnam against the government and a third of the population was soon living in areas of communist control. In December 1960, North Vietnam formally created the Viet Cong with the intent of uniting all anti-GVN insurgents, including non-communists. It was formed in Memot, Cambodia, and directed through COSVN. The Viet Cong "placed heavy emphasis on the withdrawal of American advisors and influence, on land reform and liberalization of the GVN, on coalition government and the neutralization of Vietnam." The identities of the leaders of the organization were often kept secret.

Support for the VC was driven by resentment of Diem's reversal of Viet Minh land reforms in the countryside. The Viet Minh had confiscated large private landholdings, reduced rents and debts, and leased communal lands, mostly to poorer peasants. Diem brought the landlords back, people who had been farming land for years had to return it to landlords and pay years of back rent. Marilyn B. Young wrote that "The divisions within villages reproduced those that had existed against the French: 75% support for the NLF, 20% trying to remain neutral and 5% firmly pro-government".

In March 1956, southern communist leader Lê Duẩn presented a plan to revive the insurgency entitled "The Road to the South" to the Politburo in Hanoi. However, as China and the Soviets opposed confrontation, his plan was rejected. Despite this, the North Vietnamese leadership approved tentative measures to revive southern insurgency in December 1956. Communist forces were under a single command structure set up in 1958. In May 1958, North Vietnamese forces seized the transportation hub at Tchepone in Southern Laos near the demilitarized zone, between North and South Vietnam.

The North Vietnamese Communist Party approved a "people's war" on the South at a session in January 1959, and, in May, Group 559 was established to maintain and upgrade the Ho Chi Minh trail, at this time a six-month mountain trek through Laos. On 28 July, North Vietnamese and Pathet Lao forces invaded Laos, fighting the Royal Lao Army all along the border. About 500 of the "regroupees" of 1954 were sent south on the trail during its first year of operation. The first arms delivery via the trail was completed in August 1959. In April 1960, North Vietnam imposed universal military conscription for men. About 40,000 communist soldiers infiltrated the south from 1961 to 1963.

In the 1960 U.S. presidential election, Senator John F. Kennedy defeated incumbent Vice President Richard Nixon. Although Eisenhower warned Kennedy about Laos and Vietnam, Europe and Latin America "loomed larger than Asia on his sights." In June 1961, he bitterly disagreed with Soviet premier Nikita Khrushchev when they met in Vienna to discuss key U.S.–Soviet issues. Only 16 months later, the Cuban Missile Crisis (October 1962) played out on television worldwide. It was the closest the Cold War came to nuclear war.

The Kennedy administration remained committed to the Cold War foreign policy inherited from the Truman and Eisenhower administrations. In 1961, the US had 50,000 troops based in South Korea, and Kennedy faced four crisis situations: the failure of the Bay of Pigs Invasion he had approved in April, settlement negotiations between the pro-Western government of Laos and the Pathet Lao communist movement in May, construction of the Berlin Wall in August, and the Cuban Missile Crisis in October. Kennedy believed another failure to stop communist expansion would irreparably damage US credibility. He was determined to "draw a line in the sand" and prevent a communist victory in Vietnam. He told James Reston of The New York Times after the Vienna summit with Khrushchev, "Now we have a problem making our power credible and Vietnam looks like the place."

Kennedy's policy toward South Vietnam assumed Diệm and his forces had to defeat the guerrillas on their own. He was against the deployment of American combat troops and observed "to introduce U.S. forces in large numbers there today, while it might have an initially favorable military impact, would almost certainly lead to adverse political and, in the long run, adverse military consequences." The quality of the South Vietnamese military, however, remained poor. Poor leadership, corruption, and political promotions weakened the ARVN. The frequency of guerrilla attacks rose as the insurgency gathered steam. While Hanoi's support for the Viet Cong played a role, South Vietnamese governmental incompetence was at the core of the crisis.

One major issue Kennedy raised was whether the Soviet space and missile programs had surpassed those of the US. Although Kennedy stressed long-range missile parity with the Soviets, he was interested in using special forces for counterinsurgency warfare in Third World countries threatened by communist insurgencies. Although they were intended for use behind front lines after a conventional Soviet invasion of Europe, Kennedy believed guerrilla tactics employed by special forces, such as the Green Berets, would be effective in a "brush fire" war in Vietnam.

Kennedy advisors Maxwell Taylor and Walt Rostow recommended US troops be sent to South Vietnam disguised as flood relief workers. Kennedy rejected the idea but increased military assistance. In April 1962, John Kenneth Galbraith warned Kennedy of the "danger we shall replace the French as a colonial force in the area and bleed as the French did." Eisenhower put 900 advisors in Vietnam, and by November 1963, Kennedy had put 16,000 military personnel there.

The Strategic Hamlet Program was initiated in late 1961. This joint U.S.–South Vietnamese program attempted to resettle the rural population into fortified villages. It was implemented in early 1962 and involved some forced relocation and segregation of rural South Vietnamese, into new communities where the peasantry would be isolated from the Viet Cong. It was hoped these new communities would provide security for the peasants and strengthen the tie between them and the central government. However, by November 1963 the program had waned, and it ended in 1964. In July 1962, 14 nations, including China, South Vietnam, the Soviet Union, North Vietnam, and the US, signed an agreement promising to respect Laos' neutrality.

The inept performance of the ARVN was exemplified by failed actions such as the Battle of Ấp Bắc on 2 January 1963, in which a band of Viet Cong won a battle against a much larger and better-equipped South Vietnamese force, many of whose officers seemed reluctant even to engage in combat. The South Vietnamese lost 83 soldiers and 5 US war helicopters, serving to ferry troops shot down by Vietcong forces, while the Vietcong lost only 18 soldiers. The ARVN forces were led by Diệm's most trusted general, Huỳnh Văn Cao. Cao was a Catholic, promoted due to religion and fidelity rather than skill, and his main job was to preserve his forces to stave off coups. Policymakers in Washington began to conclude Diệm was incapable of defeating the communists and might even make a deal with Ho Chi Minh. He seemed concerned only with fending off coups and had become paranoid after attempts in 1960 and 1962, which he partly attributed to US encouragement. As Robert F. Kennedy noted, "Diệm wouldn't make even the slightest concessions. He was difficult to reason with ..." Historian James Gibson summed up the situation:

Strategic hamlets had failed ... The South Vietnamese regime was incapable of winning the peasantry because of its class base among landlords. Indeed, there was no longer a 'regime' in the sense of a relatively stable political alliance and functioning bureaucracy. Instead, civil government and military operations had virtually ceased. The National Liberation Front had made great progress and was close to declaring provisional revolutionary governments in large areas.

Discontent with Diệm's policies exploded in May 1963, following the Huế Phật Đản shootings of 9 Buddhists protesting the ban on displaying the Buddhist flag on Vesak, Buddha's birthday. This resulted in mass protests -the Buddhist crisis- against discriminatory policies that gave privileges to Catholics over the Buddhist majority. Diệm's elder brother Ngô Đình Thục was the Archbishop of Huế and aggressively blurred the separation between church and state. Thuc's anniversary celebrations occurred shortly before Vesak had been bankrolled by the government, and Vatican flags were displayed prominently. There had been reports of Catholic paramilitaries demolishing Buddhist pagodas throughout Diệm's rule. Diệm refused to make concessions to the Buddhist majority or take responsibility for the deaths. On 21 August 1963, the ARVN Special Forces of Colonel Lê Quang Tung, loyal to Diệm's younger brother Ngô Đình Nhu, raided pagodas, causing widespread destruction and leaving a death toll into the hundreds.

US officials began discussing regime change during the middle of 1963. The United States Department of State wanted to encourage a coup, while the Pentagon favored Diệm. Chief among the proposed changes was removal of Diệm's younger brother Nhu, who controlled the secret police and special forces, and was seen as being behind the Buddhist repression and the architect of the Ngô family's rule. This proposal was conveyed to the US embassy in Saigon in Cable 243. The CIA contacted generals planning to remove Diệm, and told them the US would not oppose such a move, nor punish them by cutting off aid. Diệm was executed, along with his brother, on 2 November 1963. When Kennedy was informed, Maxwell Taylor remembered he "rushed from the room with a look of shock and dismay on his face." Kennedy had not anticipated Diệm's murder. The U.S. ambassador Henry Cabot Lodge, invited the coup leaders to the embassy and congratulated them. Lodge informed Kennedy that "the prospects now are for a shorter war". Kennedy wrote Lodge a letter congratulating him for "a fine job".

Following the coup, chaos ensued. Hanoi took advantage and increased its support for the guerrillas. South Vietnam entered extreme political instability, as one military government toppled another in quick succession. Increasingly, each new regime was viewed by the communists as a puppet of the Americans; whatever the failings of Diệm, his credentials as a nationalist had been impeccable. US advisors were embedded at every level of the South Vietnamese armed forces. They were however criticized for ignoring the political nature of the insurgency. The Kennedy administration sought to refocus US efforts on pacification – which in this case was defined as countering the growing threat of insurgency – and "winning the hearts and minds" of the population. Military leadership in Washington, however, was hostile to any role for U.S. advisors other than troop training. General Paul Harkins, the commander of U.S. forces in South Vietnam, confidently predicted victory by Christmas 1963. The CIA was less optimistic, however, warning that "the Viet Cong by and large retain de facto control of much of the countryside and have steadily increased the overall intensity of the effort".

Paramilitary officers from the CIA's Special Activities Division trained and led Hmong tribesmen in Laos and into Vietnam. The indigenous forces were in the tens of thousands and conducted direct action missions, led by paramilitary officers, against the Communist Pathet Lao forces and their North Vietnamese supporters. The CIA ran the Phoenix Program and participated in the Military Assistance Command, Vietnam – Studies and Observations Group (MAC-V SOG).

President Kennedy was assassinated on 22 November 1963. Vice President Lyndon B. Johnson had not been heavily involved with policy toward Vietnam; however, upon becoming president, he immediately focused it. On 24 November 1963, he said, "the battle against communism ... must be joined ... with strength and determination." Johnson knew he had inherited a deteriorating situation in South Vietnam, but adhered to the widely accepted domino argument for defending the South: Should they retreat or appease, either action would imperil other nations. Findings from RAND's Viet Cong Motivation and Morale Project bolstered his confidence that an air war would weaken the Viet Cong. Some argue the policy of North Vietnam was not to topple other non-communist governments in South East Asia.

The military revolutionary council, meeting in lieu of a strong South Vietnamese leader, had 12 members. It was headed by General Dương Văn Minh, whom journalist Stanley Karnow, recalled as "a model of lethargy". Lodge cabled home about Minh: "Will he be strong enough to get on top of things?" Minh's regime was overthrown in January 1964 by General Nguyễn Khánh. There was persistent instability in the military: several coups—not all successful—occurred in a short period of time.

On 2 August 1964, USS Maddox, on an intelligence mission along North Vietnam's coast, fired upon and damaged torpedo boats approaching it in the Gulf of Tonkin. A second attack was reported two days later on USS Turner Joy and Maddox. The circumstances were murky. Johnson commented to Undersecretary of State George Ball that "those sailors out there may have been shooting at flying fish." An NSA publication declassified in 2005 revealed there was no attack on 4 August.

The second "attack" led to retaliatory airstrikes, and prompted Congress to approve the Gulf of Tonkin Resolution on 7 August 1964. The resolution granted the president power "to take all necessary measures to repel any armed attack against the forces of the United States and to prevent further aggression" and Johnson relied on this as giving him authority to expand the war. Johnson pledged he was not "committing American boys to fighting a war that I think ought to be fought by the boys of Asia to help protect their own land".

The National Security Council recommended a three-stage escalation of the bombing of North Vietnam. Following an attack on a U.S. Army base on 7 February 1965, airstrikes were initiated, while Soviet Premier Alexei Kosygin was on a state visit to North Vietnam. Operation Rolling Thunder and Operation Arc Light expanded aerial bombardment and ground support operations. The bombing campaign, which lasted 3 years, was intended to force North Vietnam to cease its support for the Viet Cong by threatening to destroy North Vietnamese air defenses and infrastructure. It was additionally aimed at bolstering South Vietnamese morale. Between March 1965 and November 1968, Rolling Thunder deluged the north with a million tons of missiles, rockets and bombs.

Bombing was not restricted to North Vietnam. Other aerial campaigns, targeted different parts of the Viet Cong and PAVN infrastructure. These included the Ho Chi Minh trail supply route, which ran through Laos and Cambodia. The ostensibly neutral Laos had become the scene of a civil war, pitting the Laotian government backed by the US, against the Pathet Lao and its North Vietnamese allies.

Massive aerial bombardment against the Pathet Lao and PAVN forces was carried out by the US to prevent the collapse of the Royal central government, and deny use of the Ho Chi Minh Trail. Between 1964 and 1973, the U.S. dropped two million tons of bombs on Laos, nearly equal to the 2.1 million tons of bombs it dropped on Europe and Asia during World War II, making Laos the most heavily bombed country in history, relative to its population.

The objective of stopping North Vietnam and the Viet Cong was never reached. The Chief of Staff of the United States Air Force Curtis LeMay, however, had long advocated saturation bombing in Vietnam and wrote of the communists that "we're going to bomb them back into the Stone Age".

Following the Gulf of Tonkin Resolution, Hanoi anticipated the arrival of US troops and began expanding the Viet Cong, as well as sending increasing numbers of North Vietnamese personnel southwards. They were outfitting the Viet Cong forces and standardizing their equipment with AK-47 rifles and other supplies, as well as forming the 9th Division. "From a strength of approximately 5,000 at the start of 1959 the Viet Cong's ranks grew to about 100,000 at the end of 1964 ... Between 1961 and 1964 the Army's strength rose from about 850,000 to nearly a million men." U.S. troop numbers deployed to Vietnam during the same period were much lower: 2,000 in 1961, rising to 16,500 in 1964. The use of captured equipment decreased, while greater numbers of ammunition and supplies were required to maintain regular units. Group 559 was tasked with expanding the Ho Chi Minh trail, in light of the bombardment by US warplanes. The war had shifted into the final, conventional phase of Hanoi's three-stage protracted warfare model. The Viet Cong was now tasked with destroying the ARVN and capturing and holding areas; however, it was not yet strong enough to assault major towns and cities.

In December 1964, ARVN forces suffered heavy losses at the Battle of Bình Giã, in a battle both sides viewed as a watershed. Previously, the VC had utilized hit-and-run guerrilla tactics. At Binh Gia, however, they defeated a strong ARVN force in a conventional battle and remained in the field for four days. Tellingly, South Vietnamese forces were again defeated in June 1965 at the Battle of Đồng Xoài.

On 8 March 1965, 3,500 U.S. Marines were landed near Da Nang, South Vietnam. This marked the beginning of the American ground war. U.S. public opinion overwhelmingly supported the deployment. The Marines' initial assignment was defense of Da Nang Air Base. The first deployment of 3,500 in March 1965 was increased to nearly 200,000 by December. U.S. military had long been schooled in offensive warfare. Regardless of political policies, U.S. commanders were institutionally and psychologically unsuited to a defensive mission.

General William Westmoreland informed Admiral U. S. Grant Sharp Jr., commander of U.S. Pacific forces, that the situation was critical, "I am convinced that U.S. troops with their energy, mobility, and firepower can successfully take the fight to the NLF (Viet Cong)". With this recommendation, Westmoreland was advocating an aggressive departure from America's defensive posture and the sidelining of the South Vietnamese. By ignoring ARVN units, the U.S. commitment became open-ended. Westmoreland outlined a three-point plan to win the war:

• Phase 1. Commitment of U.S. and allied forces necessary to halt the losing trend by the end of 1965.
• Phase 2. U.S. and allied forces mount major offensive actions to seize the initiative to destroy guerrilla and organized enemy forces. This phase would end when the enemy had been worn down and driven back from major populated areas.
• Phase 3. If the enemy persisted, a period of 12–18 months following Phase 2 would be required for final destruction of enemy forces remaining in remote base areas.

The plan was approved by Johnson and marked a profound departure from the insistence that South Vietnam was responsible for defeating the guerrillas. Westmoreland predicted victory by the end of 1967. Johnson did not communicate this change in strategy to the media. Instead he emphasized continuity. The change in policy depended on matching the North Vietnamese and Viet Cong in a contest of attrition and morale. The opponents were locked in a cycle of escalation. Westmoreland and McNamara touted the body count system for gauging victory, a metric that would prove flawed.

The American buildup transformed the South Vietnamese economy and had a profound effect on society. South Vietnam was inundated with manufactured goods. Washington encouraged its SEATO allies to contribute troops; Australia, New Zealand, Thailand, and the Philippines agreed to do so. South Korea would ask to join the Many Flags program in return for economic compensation. Major allies, however, notably NATO countries Canada and the UK, declined troop requests.

The U.S. and its allies mounted complex search and destroy operations. In November 1965, the U.S. engaged in its first major battle with the PAVN, the Battle of Ia Drang. The operation was the first large scale helicopter air assault by the U.S., and first to employ Boeing B-52 Stratofortress strategic bombers in support. These tactics continued in 1966–67, however, the PAVN/VC insurgents remained elusive and demonstrated tactical flexibility. By 1967, the war had generated large-scale internal refugees, 2 million in South Vietnam, with 125,000 people evacuated and rendered homeless during Operation Masher alone, which was the largest search and destroy operation to that point. Operation Masher would have negligible impact, however, as the PAVN/VC returned to the province just four months after it ended. Despite major operations, which the Viet Cong and PAVN would typically evade, the war was characterized by smaller-unit contacts or engagements. The Viet Cong and PAVN would initiate 90% of large firefights, and thus the PAVN/Viet Cong would retain strategic initiative despite overwhelming US force and fire-power deployment. The PAVN and Viet Cong had developed strategies capable of countering US military doctrines and tactics: see NLF and PAVN battle tactics.

Meanwhile, the political situation in South Vietnam began to stabilize with the arrival of prime minister Air Marshal Nguyễn Cao Kỳ and figurehead chief of state, General Nguyễn Văn Thiệu, in mid-1965 at the head of a junta. In 1967, Thieu became president with Ky as his deputy, after rigged elections. Although they were nominally a civilian government, Ky was supposed to maintain real power through a behind-the-scenes military body. However, Thieu outmanoeuvred and sidelined Ky. Thieu was accused of murdering Ky loyalists through contrived military accidents. Thieu remained president until 1975, having won a one-candidate election in 1971.

Johnson employed a "policy of minimum candor" with the media. Military information officers sought to manage coverage by emphasizing stories that portrayed progress. This policy damaged the public trust in official pronouncements. As coverage of the war and the Pentagon diverged, a so-called credibility gap developed. Despite Johnson and Westmoreland publicly proclaiming victory and Westmoreland stating the "end is coming into view", internal reports in the Pentagon Papers indicate that Viet Cong forces retained strategic initiative and controlled their losses. Viet Cong attacks against static US positions accounted for 30% of engagements, Viet Cong/PAVN ambushes and encirclements for 23%, American ambushes against Viet Cong/PAVN forces for 9%, and American forces attacking Viet Cong emplacements only 5%.

Types of Engagements, From Department of Defence Study 1967

TYPE OF ENGAGEMENTS IN COMBAT NARRATIVES	Percentage of Total Engagements	Notes
Hot Landing Zone. VC/PAVN Attacks U.S. Troops As They Deploy	13	Planned VC/PAVN Attacks Are 66% Of All Engagements
Planned VC/PAVN Attack Against US Defensive Perimeter	30
VC/PAVN Ambushes or Encircles A Moving US Unit	23
Unplanned US Attacks On A VC/PAVN Defensive Perimeter, Engagement A Virtual Surprise To US Commanders	13	Defensive Posts Being Well Concealed or VC/PAVN Alerted or Anticipated
Planned US Attack Against Known VC/PAVN Defensive Perimeter	5	Planned US Attacks Against VC/PAVN Represent 14% Of All Engagements
U.S. Forces Ambushes Moving VC/PAVN Units	9
Chance Engagement, Neither Side Planned	7

In late 1967, the PAVN lured American forces into the hinterlands at Đắk Tô and at the Marine Khe Sanh combat base, where the U.S. fought The Hill Fights. These were part of a diversionary strategy meant to draw US forces towards the Central Highlands. Preparations were underway for the Tet Offensive, with the intention of Văn Tiến Dũng forces to launch "direct attacks on the American and puppet nerve centers—Saigon, Huế, Danang, all the cities, towns and main bases ..." Le Duan sought to placate critics of the stalemate by planning a decisive victory. He reasoned this could be achieved through sparking an uprising within the towns and cities, along with mass defections among ARVN units, who were on leave during the truce period.

The Tet Offensive began on 30 January 1968, as over 100 cities were attacked by over 85,000 VC/PAVN troops, including assaults on military installations, headquarters, and government buildings, including the U.S. Embassy in Saigon. U.S. and South Vietnamese forces were shocked by the scale, intensity and deliberative planning, as infiltration of personnel and weapons into the cities was accomplished covertly; the offensive constituted an intelligence failure on the scale of Pearl Harbor. Most cities were recaptured within weeks, except the former imperial capital Huế, which PAVN/Viet Cong troops held on for 26 days. They executed approximately 2,800 unarmed Huế civilians and foreigners they considered to be spies. In the following Battle of Huế American forces employed massive firepower that left 80% of the city in ruins. At Quảng Trị City, the ARVN Airborne Division, the 1st Division and a regiment of the US 1st Cavalry Division managed to hold out and overcome an assault intended to capture the city. In Saigon, Viet Cong/PAVN fighters had captured areas in and around the city, attacking key installations before US and ARVN forces dislodged them after three weeks. During one battle, Peter Arnett reported an infantry commander saying of the Battle of Bến Tre that "it became necessary to destroy the village in order to save it."

During the first month of the offensive, 1,100 Americans and other allied troops, 2,100 ARVN and 14,000 civilians were killed. After two months, nearly 5,000 ARVN and over 4,000 U.S. forces had been killed and 45,820 wounded. The U.S. claimed 17,000 of the PAVN and Viet Cong had been killed and 15,000 wounded. A month later a second offensive known as the May Offensive was launched; it demonstrated the Viet Cong were still capable of carrying out orchestrated nationwide offensives. Two months later a third offensive was launched, Phase III Offensive. PAVN records of their losses across all three offensives was 45,267 killed and 111,179 total casualties. It had become the bloodiest year up to then. The failure to spark a general uprising and lack of defections among the ARVN units meant both war goals of Hanoi had fallen flat at enormous cost.

Prior to Tet, in November 1967, Westmoreland had spearheaded a public relations drive for the Johnson administration to bolster flagging public support. In a speech to the National Press Club he said a point had been reached "where the end comes into view." Thus, the public was shocked and confused when Westmoreland's predictions were trumped by the Tet Offensive. Public approval of his performance dropped from 48% to 36%, and endorsement for the war fell from 40% to 26%." The public and media began to turn against Johnson as the offensives contradicted claims of progress.

At one point in 1968, Westmoreland considered the use of nuclear weapons in a contingency plan codenamed Fracture Jaw, which was abandoned when it became known to the White House. Westmoreland requested 200,000 additional troops, which was leaked to the media, and the fallout combined with intelligence failures caused him to be removed from command in March 1968, succeeded by his deputy Creighton Abrams.

On 10 May 1968, peace talks began between the US and North Vietnam in Paris. Negotiations stagnated for five months, until Johnson gave orders to halt the bombing of North Vietnam. Hanoi realized it could not achieve a "total victory" and employed a strategy known as "talking while fighting, fighting while talking", in which offensives would occur concurrently with negotiations.

Johnson declined to run for re-election as his approval rating slumped from 48% to 36%. His escalation of the war divided Americans, cost 30,000 American lives by that point and was regarded to have destroyed his presidency. Refusal to send more troops was seen as Johnson's admission that the war was lost. As Secretary of Defense Robert McNamara said, "the dangerous illusion of victory by the United States was therefore dead."

Vietnam was a major political issue during the United States presidential election in 1968. The election was won by Republican Richard Nixon who claimed to have a secret plan to end the war.

President Nixon began troop withdrawals in 1969. His plan to build up the ARVN so it could take over the defense of South Vietnam became known as "Vietnamization". As the PAVN/VC recovered from their 1968 losses and avoided contact, Creighton Abrams conducted operations aimed at disrupting logistics, with better use of firepower and more cooperation with the ARVN. In October 1969, Nixon had ordered B-52s loaded with nuclear weapons to race to the border of Soviet airspace to convince the Soviet Union, in accord with the madman theory, he was capable of anything to end the Vietnam War. Nixon had sought détente with the Soviet Union and rapprochement with China, which decreased tensions and led to nuclear arms reductions. However, the Soviets continued to supply the North Vietnamese.

In September 1969, Ho Chi Minh died aged 79. The failure of the 1968 Tet Offensive to spark a popular uprising in the south caused a shift in Hanoi's war strategy, and the Giáp-Chinh "Northern-First" faction regained control over military affairs from the Lê Duẩn-Hoàng Văn Thái "Southern-First" faction. An unconventional victory was sidelined in favor of a conventional victory through conquest. Large-scale offensives were rolled back in favor of small-unit and sapper attacks as well as targeting the pacification and Vietnamization strategy. Following Tet, the PAVN had transformed from a light-infantry, limited mobility force into a high-mobile and mechanized combined arms force. By 1970, over 70% of communist troops in the south were northerners, and southern-dominated VC units no longer existed.

The anti-war movement was gaining strength in the US. Nixon appealed to the "silent majority" who he said supported the war without showing it. But revelations of the 1968 My Lai Massacre, in which a US Army unit under Captain Ernest Medina raped and killed civilians, and the 1969 "Green Beret Affair", where 8 Special Forces soldiers, were arrested for the murder of a suspected double agent, provoked national and international outrage.

In 1971, the Pentagon Papers were leaked to The New York Times. The top-secret history of US involvement in Vietnam, commissioned by the Department of Defense, detailed public deceptions on the part of the government. The Supreme Court ruled its publication was legal.

Following the Tet Offensive and decreasing support among the US public, US forces began a period of morale collapse, and disobedience. At home, desertion rates quadrupled from 1966 levels. Among the enlisted, only 2.5% chose infantry combat positions in 1969–70. ROTC enrollment decreased from 191,749 in 1966 to 72,459 by 1971, and reached a low of 33,220 in 1974, depriving US forces of much-needed military leadership.

Open refusal to engage in patrols or carry out orders emerged, with a notable case of an entire company refusing orders to carry out operations. Unit cohesion began to dissipate and focused on minimizing contact with Viet Cong and PAVN. A practice known as "sand-bagging" started, where units ordered to patrol would go into the country-side, find a site out of view from superiors and radio in false coordinates and unit reports. Drug usage increased among US forces, 30% regularly used marijuana, while a House subcommittee found 10% regularly used high-grade heroin. From 1969 on, search-and-destroy operations became referred to as "search and avoid" operations, falsifying battle reports while avoiding guerrillas. 900 fragging and suspected fragging incidents were investigated, most occurring between 1969 and 1971. In 1969, field-performance was characterized by lowered morale, lack of motivation, and poor leadership. The significant decline in US morale was demonstrated by the Battle of FSB Mary Ann in March 1971, in which a sapper attack inflicted serious losses on the U.S. defenders. William Westmoreland, no longer in command but tasked with investigation of the failure, cited a dereliction of duty, lax defensive postures and lack of officers in charge.

On the collapse of morale, historian Shelby Stanton wrote:

In the last years of the Army's retreat, its remaining forces were relegated to static security. The American Army's decline was readily apparent in this final stage. Racial incidents, drug abuse, combat disobedience, and crime reflected growing idleness, resentment, and frustration ... the fatal handicaps of faulty campaign strategy, incomplete wartime preparation, and the tardy, superficial attempts at Vietnamization. An entire American army was sacrificed on the battlefield of Vietnam.

Beginning in 1969, American troops were withdrawn from border areas where most of the fighting took place and redeployed along the coast and interior. US casualties in 1970 were less than half of 1969, after being relegated to less active combat. While US forces were redeployed, the ARVN took over combat operations, with casualties double US casualties in 1969, and more than triple US ones in 1970. In the post-Tet environment, membership in the South Vietnamese Regional Force and Popular Force militias grew, and they were now more capable of providing village security, which the Americans had not accomplished.

In 1970, Nixon announced the withdrawal of an additional 150,000 American troops, reducing US numbers to 265,500. By 1970, Viet Cong forces were no longer southern-majority, nearly 70% of units were northerners. Between 1969 and 1971 the Viet Cong and some PAVN units had reverted to small unit tactics typical of 1967 and prior, instead of nationwide offensives. In 1971, Australia and New Zealand withdrew their soldiers and US troops were further reduced to 196,700, with a deadline to remove another 45,000 troops by February 1972. The US reduced support troops, and in March 1971 the 5th Special Forces Group, the first American unit deployed to South Vietnam, withdrew.

Prince Norodom Sihanouk had proclaimed Cambodia neutral since 1955, but permitted the PAVN/Viet Cong to use the port of Sihanoukville and the Sihanouk Trail. In March 1969 Nixon launched a secret bombing campaign, called Operation Menu, against communist sanctuaries along the Cambodia/Vietnam border. Only five high-ranking congressional officials were informed.

In March 1970, Prince Sihanouk was deposed by his pro-American prime minister Lon Nol, who demanded North Vietnamese troops leave Cambodia or face military action. Nol began rounding up Vietnamese civilians in Cambodia into internment camps and massacring them, provoking reactions from the North and South Vietnamese governments. In April–May 1970, North Vietnam invaded Cambodia at the request of the Khmer Rouge, following negotiations with deputy leader Nuon Chea. Nguyen Co Thach recalls: "Nuon Chea has asked for help and we have liberated five provinces of Cambodia in ten days." US and ARVN forces launched the Cambodian Campaign in May to attack PAVN and Viet Cong bases. A counter-offensive in 1971, as part of Operation Chenla II by the PAVN, would recapture most of the border areas and decimate most of Nol's forces.

The US incursion into Cambodia sparked nationwide U.S. protests as Nixon had promised to deescalate American involvement. Four students were killed by National Guardsmen in May 1970 during a protest at Kent State University, which provoked further public outrage. The reaction by the administration was seen as callous, reinvigorating the declining anti-war movement. The US Air Force continued to bomb Cambodia in support of the Cambodian government as part of Operation Freedom Deal.

Building on the success of ARVN units in Cambodia, and further testing the Vietnamization program, the ARVN were tasked with Operation Lam Son 719 in February 1971, the first major ground operation to attack the Ho Chi Minh trail, at the crossroad of Tchepone. This offensive was the first time the PAVN would field-test its combined arms force. The first few days were a success, but momentum slowed after fierce resistance. Thiệu had halted the general advance, leaving armored divisions able to surround them.

Thieu ordered air assault troops to capture Tchepone and withdraw, despite facing four-times larger numbers. During the withdrawal, the PAVN counterattack had forced a panicked rout. Half of the ARVN troops were either captured or killed, half of the ARVN/US support helicopters were downed and the operation was considered a fiasco, demonstrating operational deficiencies within the ARVN. Nixon and Thieu had sought to use to showcase victory simply by capturing Tchepone, and it was spun off as an "operational success".

Vietnamization was again tested by the Easter Offensive of 1972, a conventional PAVN invasion of South Vietnam. The PAVN overran the northern provinces and attacked from Cambodia, threatening to cut the country in half. US troop withdrawals continued, but American airpower responded, beginning Operation Linebacker, and the offensive was halted. The US Navy also initiated Operation Pocket Money in May, an aerial mining campaign in Haiphong Harbor that prevented North Vietnam's allies from resupplying it with weapons and aid by sea.

The war was central to the 1972 U.S. presidential election as Nixon's opponent, George McGovern, campaigned on immediate withdrawal. Nixon's Security Advisor, Henry Kissinger, had continued secret negotiations with North Vietnam's Lê Đức Thọ and in October 1972 reached an agreement. President Thieu demanded changes to the peace accord upon its discovery, and when North Vietnam went public with the details, the Nixon administration claimed they were attempting to embarrass the president. The negotiations became deadlocked when Hanoi demanded changes. To show his support for South Vietnam and force Hanoi back to the negotiating table, Nixon ordered Operation Linebacker II, a bombing of Hanoi and Haiphong in December 1972. Nixon pressured Thieu to accept the agreement or face military action.

On 15 January 1973, all US combat activities were suspended. Lê Đức Thọ and Henry Kissinger, along with the PRG Foreign Minister Nguyễn Thị Bình and a reluctant President Thiệu, signed the Paris Peace Accords on 27 January 1973. This ended direct U.S. involvement in the Vietnam War, created a ceasefire between North Vietnam/PRG and South Vietnam, guaranteed the territorial integrity of Vietnam under the Geneva Conference of 1954, called for elections or a political settlement between the PRG and South Vietnam, allowed 200,000 communist troops to remain in the south, and agreed to a POW exchange. There was a 60-day period for the withdrawal of US forces. "This article", noted Peter Church, "proved ... to be the only one of the Paris Agreements which was fully carried out." All US forces personnel were withdrawn by March 1973.

In the lead-up to the ceasefire on 28 January, both sides attempted to maximize land and population under their control in a campaign known as the War of the flags. Fighting continued after the ceasefire, without US participation, and throughout the year. North Vietnam was allowed to continue supplying troops in the South but only to replace expended material. The Nobel Peace Prize was awarded to Kissinger and Thọ, but the North Vietnamese negotiator declined it saying true peace did not yet exist.

On 15 March 1973, Nixon implied the US would intervene militarily if the North launched a full offensive, and Secretary of Defense Schlesinger re-affirmed this during his June confirmation hearings. Public and congressional reaction to Nixon's statement was unfavorable, prompting the Senate to pass the Case–Church Amendment to prohibit any intervention.

PAVN/VC leaders expected the ceasefire terms would favor their side, but Saigon, bolstered by a surge of US aid just before the ceasefire went into effect, began to roll back the Viet Cong. The PAVN/VC responded with a new strategy hammered out in meetings in Hanoi in March 1973, according to the memoirs of Trần Văn Trà. With US bombings suspended, work on the Ho Chi Minh trail and other logistical structures could proceed. Logistics would be upgraded until the North was in a position to launch a massive invasion of the South, projected for the 1975–76 dry season. Tra calculated this date would be Hanoi's last opportunity to strike, before Saigon's army could be fully trained. The PAVN/VC resumed offensive operations when the dry season began in 1973, and by January 1974 had recaptured territory it lost during the previous dry season.

Within South Vietnam, the departure of the US and the global recession after the 1973 oil crisis hurt an economy partly dependent on US financial support and troop presence. After clashes that left 55 ARVN soldiers dead, Thieu announced on 4 January 1974, that the war had restarted and the Peace Accords were no longer in effect. There were over 25,000 South Vietnamese casualties during the ceasefire period. Gerald Ford took over as US president in August 1974, and Congress cut financial aid to South Vietnam from $1 billion a year to $700 million. Congress voted in restrictions on funding to be phased in through 1975 and then total cutoff in 1976.

The success of the 1973–1974 dry season offensive inspired Trà to return to Hanoi in October 1974 and plead for a larger offensive the next dry season. This time, Trà could travel on a drivable highway with fueling stops, a vast change from when the Ho Chi Minh trail was a dangerous mountain trek. Giáp, the North Vietnamese defense minister, was reluctant to approve Trà's plan since a larger offensive might provoke US reaction and interfere with the big push planned for 1976. Trà appealed to Giáp's superior, Lê Duẩn, who approved it. Trà's plan called for a limited offensive from Cambodia into Phước Long Province. The strike was designed to solve logistical problems, gauge the reaction of South Vietnamese forces, and determine whether the US would return. On 13 December 1974, North Vietnamese forces attacked Phước Long. Phuoc Binh fell on 6 January 1975. Ford desperately asked Congress for funds to assist and re-supply the South before it was overrun. Congress refused. The fall of Phuoc Binh and lack of American response left the South Vietnamese elite demoralized.

The speed of this success led the Politburo to reassess its strategy. It decided operations in the Central Highlands would be turned over to General Văn Tiến Dũng and that Pleiku should be seized, if possible. Dũng said to Lê Duẩn: "Never have we had military and political conditions so perfect or a strategic advantage as great as we have now." At the start of 1975, the South Vietnamese had three times as much artillery and twice as many tanks and armored cars as the PAVN. However, heightened oil prices meant many assets could not be leveraged. Moreover, the rushed nature of Vietnamization, intended to cover the US retreat, resulted in a lack of spare parts, ground-crew, and maintenance personnel, which rendered most of it inoperable.

On 10 March 1975, General Dung launched Campaign 275, a limited offensive into the Central Highlands, supported by tanks and heavy artillery. The target was Ban Ma Thuột; if the town could be taken, the provincial capital Pleiku and the road to the coast, would be exposed for a campaign in 1976. The ARVN proved incapable of resisting the onslaught, and its forces collapsed. Again, Hanoi was surprised by the speed of their success. Dung urged the Politburo to allow him to seize Pleiku immediately and turn his attention to Kon Tum. He argued that with two months of good weather until onset of the monsoon, it would be irresponsible not to take advantage.

President Thiệu, a former general, was fearful his forces would be cut off in the north by the attacking communists; Thieu ordered a retreat, which turned into a bloody rout. While the bulk of ARVN forces attempted to flee, isolated units fought desperately. ARVN general Phu abandoned Pleiku and Kon Tum and retreated toward the coast, in what became known as the "column of tears". On 20 March, Thieu reversed himself and ordered Huế, Vietnam's third-largest city, be held at all costs, and then changed policy several times. As the PAVN launched their attack, panic set in, and ARVN resistance withered. On 22 March, the PAVN opened the siege of Huế. Civilians flooded the airport and docks hoping for escape. As resistance in Huế collapsed, PAVN rockets rained down on Da Nang and its airport. By 28 March 35,000 PAVN troops were poised to attack the suburbs. By 30 March 100,000 leaderless ARVN troops surrendered as the PAVN marched through Da Nang. With the fall of the city, the defense of the Central Highlands and Northern provinces ended.

With the north half of the country under their control, the Politburo ordered Dung to launch the final offensive against Saigon. The operational plan for the Ho Chi Minh Campaign called for Saigon's capture before 1 May. Hanoi wished to avoid the coming monsoon and prevent redeployment of ARVN forces defending the capital. Northern forces, their morale boosted by their recent victories, rolled on, taking Nha Trang, Cam Ranh and Da Lat.

On 7 April, three PAVN divisions attacked Xuân Lộc, 40 miles (64 km) east of Saigon. For two bloody weeks, fighting raged as the ARVN defenders made a last stand to try to block PAVN advance. On 21 April, however, the exhausted garrison was ordered to withdraw towards Saigon. An embittered and tearful president Thieu resigned, declaring that the US had betrayed South Vietnam. In a scathing attack, he suggested Kissinger had tricked him into signing the Paris peace agreement, promising military aid that failed to materialize. Having transferred power to Trần Văn Hương on 21 April, he left for Taiwan. After having appealed unsuccessfully to Congress for $722 million in emergency aid for South Vietnam, President Ford gave a televised speech on 23 April, declaring an end to the War and US aid.

By the end of April, the ARVN had collapsed except in the Mekong Delta. Refugees streamed southward, ahead of the main communist onslaught. On 27 April, 100,000 PAVN troops encircled Saigon. The city was defended by about 30,000 ARVN troops. To hasten a collapse and foment panic, the PAVN shelled Tan Son Nhut Airport and forced its closure. With the air exit closed, large numbers of civilians had no way out.

Chaos and panic broke out as hysterical South Vietnamese officials and civilians scrambled to leave. Martial law was declared. American helicopters began evacuating South Vietnamese, US and foreign nationals from the city and the U.S. embassy compound. Operation Frequent Wind had been delayed until the last possible moment, because of Ambassador Graham Martin's belief Saigon could be held and a political settlement reached. Frequent Wind was the largest helicopter evacuation in history. It began on 29 April, in an atmosphere of desperation, as hysterical crowds of Vietnamese vied for limited space. Frequent Wind continued around the clock, as PAVN tanks breached defenses near Saigon. In the early morning of 30 April, the last US Marines evacuated the embassy by helicopter, as civilians swamped the perimeter and poured into the grounds.

On 30 April 1975, PAVN troops entered Saigon and overcame all resistance, capturing key buildings and installations. Tanks from the 2nd Corps crashed through the gates of the Independence Palace and the Viet Cong flag was raised above it. President Dương Văn Minh, who had succeeded Huong two days earlier, surrendered to Lieutenant colonel Bùi Văn Tùng, political commissar of the 203rd Tank Brigade. Minh was then escorted to Radio Saigon to announce the surrender declaration. The statement was on air at 2:30 pm.

During the course of the war a large segment of Americans became opposed to U.S. involvement. In January 1967, only 32% of Americans thought the US had made a mistake in sending troops. Public opinion steadily turned against the war following 1967 and by 1970 only a third believed the U.S. had not made a mistake by sending troops.

Early opposition to US involvement drew its inspiration from the Geneva Conference of 1954. American support of Diệm in refusing elections was seen as thwarting the democracy America claimed to support. Kennedy, while senator, opposed involvement. It is possible to specify groups who led the anti-war movement at its peak in the late 1960s and the reasons why. Many young people protested because they were being drafted, while others were against because the anti-war movement grew popular among the counterculture. Some advocates within the peace movement advocated a unilateral withdrawal of forces. Opposition to the war tended to unite groups opposed to U.S. anti-communism and imperialism, and for those involved with the New Left. Others, such as Stephen Spiro, opposed the war based on the theory of Just War. Some wanted to show solidarity with the people of Vietnam, such as Norman Morrison emulating Thích Quảng Đức.

High-profile opposition to the war increasingly turned to mass protests to shift public opinion. Riots broke out at the 1968 Democratic National Convention. After reports of American military abuses, such as the My Lai Massacre, brought attention and support to the anti-war movement, some veterans joined Vietnam Veterans Against the War. On 15 October 1969, the Vietnam Moratorium attracted millions of Americans. The fatal shooting of 4 students at Kent State University in 1970 led to nationwide university protests. Anti-war protests declined after the Paris Peace Accords and the end of the draft in January 1973, and the withdrawal of American troops.

China provided significant support for North Vietnam when the US started to intervene, including financial aid and the deployment of hundreds of thousands of military personnel in support roles. China said its military and economic aid to North Vietnam and the Viet Cong totaled $20 billion ($160 billion adjusted for 2022 prices) during the Vietnam War; included were 5 million tons of food to North Vietnam (equivalent to a year's food production), accounting for 10–15% of their food supply by the 1970s.

In the summer of 1962, Mao Zedong agreed to supply Hanoi with 90,000 rifles and guns free of charge, and starting in 1965, China began sending anti-aircraft units and engineering battalions, to repair the damage caused by American bombing. They helped man anti-aircraft batteries, rebuild roads and railroads, transport supplies, and perform other engineering works. This freed North Vietnamese army units for combat. China sent 320,000 troops and annual arms shipments worth $180 million. China claims to have caused 38% of American air losses in the war. The PRC also began financing the Khmer Rouge as a counterweight to North Vietnam. China "armed and trained" the Khmer Rouge during the civil war, and continued to aid them afterward.

The Soviet Union supplied North Vietnam with medical supplies, arms, tanks, planes, helicopters, artillery, anti-aircraft missiles and other military equipment. Soviet crews fired Soviet-made surface-to-air missiles at US aircraft in 1965. Following the dissolution of the Soviet Union in 1991, Russian officials acknowledged that the USSR had stationed up to 3,000 troops in Vietnam.

According to Russian sources, between 1953 and 1991, the hardware donated by the Soviet Union included: 2,000 tanks; 1,700 APCs; 7,000 artillery guns; over 5,000 anti-aircraft guns; 158 surface-to-air missile launchers; and 120 helicopters. In total, the Soviets sent North Vietnam annual arms shipments worth $450 million. From July 1965 to the end of 1974, fighting in Vietnam was observed by some 6,500 officers and generals, as well as more than 4,500 soldiers and sergeants of the Soviet Armed Forces, amounting to 11,000 military personnel. The KGB helped develop the signals intelligence capabilities of the North Vietnamese.

As South Vietnam was formally part of a military alliance with the US, Australia, New Zealand, France, the UK, Pakistan, Thailand and the Philippines, the alliance was invoked during the war. The UK, France and Pakistan declined to participate, and South Korea, Taiwan, and Spain were non-treaty participants.

The ethnic minority peoples of South Vietnam, like the Montagnards in the Central Highlands, the Hindu and Muslim Cham, and the Buddhist Khmer Krom, were actively recruited in the war. There was a strategy of recruitment and favorable treatment of Montagnard tribes for the Viet Cong, as they were pivotal for control of infiltration routes. Some groups split off and formed the United Front for the Liberation of Oppressed Races (FULRO) to fight for autonomy or independence. FULRO fought against the South Vietnamese and Viet Cong, later fighting against the unified Socialist Republic of Vietnam, after the fall of South Vietnam.

During the war, South Vietnamese president Diem began a program to settle ethnic Vietnamese Kinh on Montagnard lands in the Central Highlands region. This provoked a backlash from the Montagnards, some joining the Viet Cong as a result. The Cambodians under pro-China King Sihanouk and pro-American Lon Nol, supported their fellow co-ethnic Khmer Krom in South Vietnam, following an anti-ethnic Vietnamese policy. Following Vietnamization, many Montagnard groups and fighters were incorporated into the Vietnamese Rangers as border sentries.

Many war crimes took place, by both sides, including: rape, massacres of civilians, bombings of civilian targets, terrorism, torture, and murder of prisoners of war. Additional common crimes included theft, arson, and the destruction of property not warranted by military necessity.

In 1966, the Russell Tribunal was organized by a number of public figures opposed to the war led by Bertrand Russell in an effort to apply the precepts of international law to the actions of the United States and its allies in Vietnam. The tribunal found the US and its allies guilty of acts of aggression, use of weapons forbidden by the laws of war, bombardment of targets of a purely civilian character, mistreatment of prisoners, and genocide. Though the tribunal's lack of juridical authority meant its findings were largely ignored by the United States and other governments, the hearings contributed to a growing body of evidence and documentation which established the factual basis for a counter-narrative to the United States' justifications for the war and inspired future hearings, tribunals and legal investigations.

In 1968, the Vietnam War Crimes Working Group (VWCWG) was established by the Pentagon task force set up in the wake of the My Lai Massacre, to ascertain the veracity of emerging claims of US war crimes. Of the war crimes reported to military authorities, sworn statements by witnesses and status reports indicated 320 incidents had a factual basis. The substantiated cases included 7 massacres between 1967 and 1971 in which at least 137 civilians were killed; 78 further attacks targeting non-combatants resulting in at least 57 deaths, 56 wounded and 15 sexually assaulted; and 141 cases of US soldiers torturing civilian detainees, or prisoners of war with fists, sticks, bats, water or electric shock. Journalists since have documented overlooked and uninvestigated war crimes, involving every active army division, including atrocities committed by Tiger Force. R. J. Rummel estimated that American forces committed around 5,500 democidal killings between 1960 and 1972.

US forces established free-fire zones to prevent Viet Cong fighters from sheltering in South Vietnamese villages. Such practice, which involved the assumption that anyone appearing in the designated zones was an enemy combatant that could be freely targeted by weapons, was regarded by journalist Lewis Simons as "a severe violation of the laws of war". Nick Turse argues that a relentless drive toward higher body counts, widespread use of free-fire zones, rules of engagement where civilians who ran from soldiers or helicopters could be viewed as Viet Cong and disdain for Vietnamese civilians, led to massive civilian casualties and war crimes inflicted by US troops. One example cited by Turse is Operation Speedy Express, which was described by John Paul Vann as, in effect, "many Mỹ Lais". A report by Newsweek magazine suggested that at least 5,000 civilians may have been killed during six months of the operation, and there were 748 recovered weapons and an official US military body count of 10,889 enemy combatants killed.

Rummel estimated that 39,000 were killed by South Vietnam during the Diem-era in democide; for 1964–75, Rummel estimated 50,000 people were killed in democide. Thus, the total for 1954 to 1975 is about 80,000 deaths caused by South Vietnam. Benjamin Valentino estimates 110,000–310,000 deaths as a "possible case" of "counter-guerrilla mass killings" by US and South Vietnamese forces. The Phoenix Program, coordinated by the CIA and involving US and South Vietnamese security forces, was aimed at destroying the political infrastructure of the Viet Cong. The program killed 26,000 to 41,000 people, with an unknown number being innocent civilians.

Torture and ill-treatment were frequently applied by the South Vietnamese to POWs, as well as civilian prisoners. During their visit to the Con Son Prison in 1970, US congressmen Augustus Hawkins and William R. Anderson witnessed detainees either confined in minute "tiger cages" or chained to their cells, and provided with poor-quality food. American doctors inspecting the prison found many inmates suffering symptoms resulting from forced immobility and torture. During their visits to US detention facilities in 1968 and 1969, the International Red Cross recorded many cases of torture and inhumane treatment before the captives were handed over to South Vietnamese authorities. Torture was conducted by the South Vietnamese government in collusion with the CIA.

South Korean forces were accused of war crimes. One documented event was the Phong Nhị and Phong Nhất massacre where the 2nd Marine Brigade reportedly killed between 69 and 79 civilians on 12 February 1968 in Phong Nhị and Phong Nhất village, Điện Bàn District. South Korean forces are accused of perpetrating other massacres: Bình Hòa massacre, Binh Tai Massacre and Hà My massacre.

Ami Pedahzur has written that "the overall volume and lethality of Viet Cong terrorism rivals or exceeds all but a handful of terrorist campaigns waged over the last third of the twentieth century", based on the definition of terrorists as a non-state actor, and examining targeted killings and civilian deaths which are estimated at over 18,000 from 1966 to 1969. The US Department of Defense estimates the VC/PAVN had conducted 36,000 murders and 58,000 kidnappings from 1967 to 1972, c. 1973. Benjamin Valentino attributes 45,000–80,000 "terrorist mass killings" to the Viet Cong. Statistics for 1968–1972 suggest "about 80 percent of the terrorist victims were ordinary civilians and only about 20 percent were government officials, policemen, members of the self-defence forces or pacification cadres." Viet Cong tactics included frequent mortaring of civilians in refugee camps, and placing of mines on highways frequented by villagers taking goods to urban markets. Some mines were set only to go off after heavy vehicle passage, causing slaughter aboard packed civilian buses.

Notable Viet Cong atrocities include the massacre of over 3,000 unarmed civilians at Huế during the Tet Offensive and the killing of 252 civilians during the Đắk Sơn massacre. 155,000 refugees fleeing the final North Vietnamese Spring Offensive were reported to have been killed, or abducted, on the road to Tuy Hòa in 1975. PAVN and Viet Cong troops killed 164,000 civilians in democide between 1954 and 1975 in South Vietnam. North Vietnam was known for its abusive treatment of American POWs, most notably in Hỏa Lò Prison (the Hanoi Hilton), where torture was employed to extract confessions.

Women were active in a large variety of roles, making significant impacts and the war having significant impacts on them. Several million Vietnamese women served in the military and in militias, particularly in the Viet Cong, with the slogan "when war comes, even the women must fight" being widely used. These women made vital contributions on the Ho Chi Minh trail, espionage, medical care, logistical and administrative work, and sometimes direct combat. Women workers took on more roles in the economy and Vietnam saw an increase in women's rights. In Vietnam and elsewhere, women emerged as leaders of anti-war peace campaigns and made significant contributions to war journalism.

However, women still faced significant levels of discrimination during and were often targets of sexual violence and war crimes. Post-war, some Vietnamese women veterans faced difficulty reintegrating into society and having their contributions recognised, as well as advances in women's rights failing to be sustained. Portrayals of the war have been criticised for their depictions of women, both for overlooking the role women played and reducing Vietnamese women to racist stereotypes. Women are at the forefront of campaigns to deal with the war's aftermath, such as the long-terms effect of Agent Orange use and the Lai Đại Hàn.

The experience of African-American military personnel has received significant attention. The site "African-American Involvement in the Vietnam War" compiles examples, as does the work of journalist Wallace Terry whose book Bloods: An Oral History of the Vietnam War by Black Veterans, includes observations about the impact on the black community and black servicemen. He notes: the higher proportion of combat casualties among African-American servicemen than other races, the shift toward and different attitudes of black military volunteers and conscripts, the discrimination encountered by black servicemen "on the battlefield in decorations, promotion and duty assignments", as well as having to endure "the racial insults, cross-burnings and Confederate flags of their white comrades"—and the experiences faced by black soldiers stateside, during the war and after withdrawal.

Civil rights leaders protested the disproportionate casualties and overrepresentation in hazardous duty, experienced by African American servicemen, prompting reforms that were implemented beginning in 1967. As a result, by the war's completion in 1975, black casualties had declined to 13% of US combat deaths, approximately equal to percentage of draft-eligible black men, though still slightly higher than the 10% who served in the military.

Nearly all US-allied forces were armed with US weapons including the M1 Garand, M1 carbine, M14 rifle, and M16 rifle. The Australian and New Zealand forces employed the 7.62 mm L1A1 Self-Loading Rifle, with occasional use of the M16 rifle.

The PAVN, although having inherited US, French, and Japanese weapons from World War II and the First Indochina War, were largely armed and supplied by China, the Soviet Union, and its Warsaw Pact allies. Some weapons—notably anti-personnel explosives, the K-50M, and "home-made" versions of the RPG-2—were manufactured in North Vietnam. By 1969 the US Army had identified 40 rifle/carbine types, 22 machine gun types, 17 types of mortar, 20 recoilless rifle or rocket launcher types, 9 types of antitank weapons, and 14 anti-aircraft artillery weapons used by ground troops on all sides. Also in use, mostly by anti-communist forces, were 24 types of armored vehicles and self-propelled artillery, and 26 types of field artillery and rocket launchers.

The US dropped over 7 million tons of bombs on Indochina during the war, more than triple the 2.1 million tons it dropped on Europe and Asia during World War II, and more than ten times the amount during the Korean War. 500 thousand tons were dropped on Cambodia, 1 million tons on North Vietnam, and 4 million tons on South Vietnam. On a per person basis, the 2 million tons dropped on Laos make it the most heavily bombed country in history; The New York Times noted this was "nearly a ton for every person in Laos." Due to the particularly heavy impact of cluster bombs, Laos was a strong advocate of the Convention on Cluster Munitions to ban the weapons, and was host to its first meeting in 2010.

Former US Air Force official Earl Tilford recounted "repeated bombing runs of a lake in central Cambodia. The B-52s literally dropped their payloads in the lake." The Air Force ran many missions like this to secure additional funding during budget negotiations, so the tonnage expended does not directly correlate with the resulting damage.

Military deaths (1955–1975)

Year	U.S.	South Vietnam
1956–1959	4	n.a.
1960	5	2,223
1961	16	4,004
1962	53	4,457
1963	122	5,665
1964	216	7,457
1965	1,928	11,242
1966	6,350	11,953
1967	11,363	12,716
1968	16,899	27,915
1969	11,780	21,833
1970	6,173	23,346
1971	2,414	22,738
1972	759	39,587
1973	68	27,901
1974	1	31,219
1975	62	n.a.
After 1975	7	n.a.
Total	58,220	>254,256

Estimates of casualties vary, with one source suggesting up to 3.8 million violent war deaths in Vietnam for 1955 to 2002. A demographic study calculated 791,000–1,141,000 war-related deaths during the war for all of Vietnam, for military and civilians. Between 195,000 and 430,000 South Vietnamese civilians died in the war. Extrapolating from a 1969 US intelligence report, Guenter Lewy estimated 65,000 North Vietnamese civilians died. Estimates of civilian deaths caused by American bombing of North Vietnam range from 30,000 to 182,000. A 1975 US Senate subcommittee estimated 1.4 million South Vietnamese civilians casualties during the war, including 415,000 deaths. The military of South Vietnam suffered an estimated 254,256 killed between 1960 and 1974, and additional deaths from 1954 to 1959 and in 1975. Other estimates point to higher figures of 313,000 casualties.

The official US Department of Defense figure for PAVN/VC killed in Vietnam from 1965 to 1974 was 950,765. Officials believed these body count figures need to be deflated by 30 percent. Guenter Lewy asserts that one-third of the reported "enemy" killed may have been civilians, concluding that the actual number of deaths of PAVN/VC military forces was probably closer to 444,000.

According to figures released by the Vietnamese government there were 849,018 confirmed military deaths on the PAVN/VC side. The Vietnamese government released its estimate of war deaths for the more lengthy period of 1955 to 1975. This figure includes battle deaths of Vietnamese soldiers in the Laotian and Cambodian Civil Wars, in which the PAVN was a major participant. Non-combat deaths account for 30-40% of these. However, the figures do not include deaths of South Vietnamese and allied soldiers. These do not include the estimated 300,000–500,000 PAVN/VC missing in action. Vietnamese government figures estimate 1.1 million dead and 300,000 missing from 1945 to 1979, with approximately 849,000 dead and 232,000 missing from 1960 to 1975.

US reports of "enemy KIA", referred to as body count, were thought to have been subject to "falsification and glorification", and a true estimate of PAVN/VC combat deaths is difficult to assess, as US victories were assessed by having a "greater kill ratio". It was difficult to distinguish between civilians and military personnel in the Viet Cong, as many were part-time guerrillas or impressed laborers who did not wear uniforms and civilians killed were sometimes written off as enemy killed, because high enemy casualties was directly tied to promotions and commendation.

Between 275,000 and 310,000 Cambodians were estimated to have died, including between 50,000 and 150,000 combatants and civilians from US bombings. 20,000–62,000 Laotians died, and 58,281 U.S. military personnel were killed, of which 1,584 are still listed as missing as of March 2021.

On 2 July 1976, North and South Vietnam were merged to form the Socialist Republic of Vietnam. Despite speculation that the victorious North Vietnamese would, in Nixon's words, "massacre the civilians there [South Vietnam] by the millions," no mass executions took place.

However many South Vietnamese were sent to re-education camps where they endured torture, starvation, and disease while being forced to perform hard labor. According to Amnesty International, this figure varied depending on different observers: "... "50,000 to 80,000" (Le Monde, April 1978), "150,000" (Reuters from Bien Hoa, November 1977), "150,000 to 200,000" (The Washington Post, December 1978), and "300,000" (Agence France Presse from Hanoi, February 1978)." Such variations are because "Some estimates may include not only detainees but also people sent from the cities to the countryside." According to a native observer, 443,360 people had to register for a period in re-education camps in Saigon alone, and while some were released after a few days, others stayed for more than a decade. Between 1975 and 1980, more than 1 million northerners migrated south, to regions formerly in the Republic of Vietnam, while, as part of the New Economic Zones program, around 750,000 to over 1 million southerners were moved mostly to mountainous forested areas. Gabriel García Márquez, a Nobel Prize winning writer, described South Vietnam as a "False paradise" after the war, when he visited in 1980:

The cost of this delirium was stupefying: 360,000 people mutilated, a million widows, 500,000 prostitutes, 500,000 drug addicts, a million tuberculous and more than a million soldiers of the old regime, impossible to rehabilitate into a new society. Ten percent of the population of Ho Chi Minh City was suffering from serious venereal diseases when the war ended, and there were 4 million illiterates throughout the South.

The US used its security council veto to block Vietnam's UN recognition three times, an obstacle to it receiving international aid.

By 1975, the North Vietnamese had lost influence over the Khmer Rouge. Phnom Penh, Cambodia's capital, fell to the Khmer Rouge in April 1975. Under Pol Pot, the Khmer Rouge would kill 1–3 million Cambodians out of a population of around 8 million, in one of the bloodiest genocides ever.

The relationship between Vietnam and Democratic Kampuchea (Cambodia) escalated after the end of the war. In response to the Khmer Rouge taking over Phu Quoc and Tho Chu, and the belief they were responsible for the disappearance of 500 Vietnamese natives on Tho Chu, Vietnam launched a counterattack to take back these islands. After failed attempts to negotiate, Vietnam invaded Democratic Kampuchea in 1978 and ousted the Khmer Rouge, who were being supported by China, in the Cambodian–Vietnamese War. In response, China invaded Vietnam in 1979. The two countries fought a border war: the Sino-Vietnamese War. From 1978 to 1979, some 450,000 ethnic Chinese left Vietnam by boat as refugees or were deported.

The Pathet Lao overthrew the monarchy of Laos in December 1975, establishing the Lao People's Democratic Republic. The change in regime was "quite peaceful, a sort of Asiatic 'velvet revolution'"—although 30,000 former officials were sent to reeducation camps, often enduring harsh conditions.

Unexploded ordnance, mostly from US bombing, continues to kill people, and has rendered much land hazardous and impossible to cultivate. Ordnance has killed 42,000 people since the war ended. In Laos, 80 million bombs failed to explode and still remain. Unexploded ordnance has killed or injured over 20,000 Laotians since the war and about 50 people are killed or maimed annually. It is estimated the explosives buried will not be removed entirely for centuries.

Over 3 million people left Vietnam, Laos, and Cambodia in the Indochina refugee crisis after 1975. Most Asian countries were unwilling to accept them, many of whom fled by boat and were known as boat people. Between 1975 and 1998, an estimated 1.2 million refugees from Vietnam and other Southeast Asian countries resettled in the US, while Canada, Australia, and France resettled over 500,000, China accepted 250,000 people. Laos experienced the largest refugee flight proportionally, 300,000 out of a population of 3 million crossed the border into Thailand. Included among their ranks were "about 90%" of Laos' "intellectuals, technicians, and officials." An estimated 200,000 to 400,000 Vietnamese boat people died at sea, according to the United Nations High Commissioner for Refugees.

Failure of US goals is often placed at different institutions and levels. Some have suggested it was due to political failures of leadership. Others point to a failure of military doctrine. Secretary of Defense Robert McNamara stated that "the achievement of a military victory by U.S. forces in Vietnam was indeed a dangerous illusion." The inability to bring Hanoi to the bargaining table by bombing illustrated another US miscalculation, and the limitations of military abilities in achieving political goals. Army Chief of Staff Harold Keith Johnson noted, "if anything came out of Vietnam, it was that air power couldn't do the job." General William Westmoreland admitted bombing had been ineffective, saying he doubted "that the North Vietnamese would have relented." Kissinger wrote in a memo to President Ford that "in terms of military tactics ... our armed forces are not suited to this kind of war. Even the Special Forces who had been designed for it could not prevail." Hanoi had persistently sought unification since the Geneva Accords, and the effects of US bombing had negligible impact on North Vietnam's goals. US bombing mobilized people throughout North Vietnam and international support, due to the perception of a superpower attempting to bomb a significantly smaller, agrarian society into submission.

In the post-war era, Americans struggled to absorb the lessons of the military intervention. President Ronald Reagan coined the term "Vietnam Syndrome" to describe the reluctance of the American public and politicians to support military interventions abroad. US polling in 1978 revealed nearly 72% of Americans believed the war was "fundamentally wrong and immoral." Six months after the beginning of Operation Rolling Thunder, Gallup, Inc. found 60% of Americans did not believe that sending troops to Vietnam was a mistake in September 1965, and only 24% believed it was. Subsequent polling did not find that a plurality of Americans believed that sending troops was a mistake until October 1967, and did not find a majority believing it was until August 1968, during the third phase of the Tet Offensive. Thereafter, Gallup found majorities believing sending troops was a mistake through the signing of the Peace Accords in January 1973, when 60% believed sending troops was a mistake, and retrospective polls by Gallup between 1990 and 2000, found 69-74% of Americans believed sending troops was a mistake. The Vietnam War POW/MIA issue, concerning the fate of US service personnel listed as missing in action, persisted for years afterwards. The costs loom large in American consciousness; a 1990 poll showed the public incorrectly believed more Americans died in Vietnam than World War II.

US expenditures in South Vietnam (1953–74)
Direct costs only

Military costs	Military aid	Economic aid	Total	Total (2015 dollars)
$111 billion	$16 billion	$7 billion	$135 billion	$1 trillion

Between 1953 and 1975, the US was estimated to have spent $168 billion on the war (equivalent to $1.7 trillion in 2023). This resulted in a large budget deficit. Other figures point to $139 billion from 1965 to 1974 (not inflation-adjusted), 10 times all education spending in the US, and 50 times more than housing and community development spending within that period. It was stated that war-spending could have paid off every mortgage in the US, with money leftover. As of 2013, the US government pays Vietnam veterans and their families more than $22 billion a year in war-related claims.

More than 3 million Americans served in the war, 1.5 million of whom saw combat. James Westheider wrote that "At the height of American involvement in 1968, for example, 543,000 American military personnel were stationed in Vietnam, but only 80,000 were considered combat troops." Conscription in the US existed since World War II, but ended in 1973.

58,220 American soldiers were killed, more than 150,000 wounded, and at least 21,000 permanently disabled. The average age of US troops killed was 23. According to Dale Kueter, "Of those killed in combat, 86% were white, 13% were black..." Approximately 830,000 veterans, 15%, suffered posttraumatic stress disorder. This unprecedented number was because the military had routinely provided heavy psychoactive drugs to servicemen, which left them unable to process trauma. Drug use, racial tensions, and the growing incidence of fragging—attempting to kill unpopular officers with grenades or other weapons—created problems for the military and impacted its capability to undertake operations. 125,000 Americans left for Canada to avoid the draft, and approximately 50,000 servicemen deserted. In 1977, President Jimmy Carter granted an unconditional pardon to all Vietnam-era draft evaders with Proclamation 4483.

The war called into question army doctrine. Marine general Victor H. Krulak criticized Westmoreland's attrition strategy, calling it "wasteful of American lives ... with small likelihood of a successful outcome." Doubts surfaced about the ability of the military to train foreign forces. There was found to be considerable flaws and dishonesty by commanders, due to promotions being tied to the body count system touted by Westmoreland and McNamara. Secretary of Defense McNamara wrote to President Johnson his doubts: "The picture of the world's greatest superpower killing or seriously injuring 1,000 noncombatants a week, while trying to pound a tiny backward nation into submission on an issue whose merits are hotly disputed, is not a pretty one."

One of the most controversial aspects of the US military effort, was the widespread use of chemical defoliants between 1961 and 1971. 20 million gallons of toxic herbicides (like Agent Orange) were sprayed on 6 million acres of forests and crops by the air force. They were used to defoliate large parts of the countryside to prevent the Viet Cong from being able to hide weaponry and encampments under the foliage, and deprive them of food. Defoliation was used to clear sensitive areas, including base perimeters and possible ambush sites along roads and canals. More than 20% of South Vietnam's forests and 3% of its cultivated land was sprayed at least once. 90% of herbicide use was directed at forest defoliation. The chemicals used continue to change the landscape, cause diseases and birth defects, and poison the food chain. US military records have listed figures including the destruction of 20% of the jungles of South Vietnam and 20-36% of the mangrove forests. The environmental destruction caused was described by Swedish Prime Minister Olof Palme, lawyers, historians and other academics as an ecocide.

Agent Orange and similar chemical substances used by the US have caused many deaths and injuries in the intervening years, including among the US Air Force crews that handled them. Scientific reports have concluded that refugees exposed to chemical sprays while in South Vietnam continued to experience pain in the eyes and skin as well as gastrointestinal upsets. In one study, 92% of participants suffered incessant fatigue; others reported monstrous births. Analysis of studies on the association between Agent Orange and birth defects, have found a statistically significant correlation such that having a parent who was exposed to Agent Orange at any point, will increase one's likelihood of possessing or acting as a genetic carrier of birth defects. The most common deformity appears to be spina bifida. There is substantial evidence that birth defects carry on for three generations or more. In 2012, the US and Vietnam began a cooperative cleaning toxic chemicals on Danang International Airport, marking the first time Washington has been involved in cleaning up Agent Orange in Vietnam.

Vietnamese victims affected by Agent Orange attempted a class action lawsuit against Dow Chemical and other US chemical manufacturers, but a US District Court dismissed their case. They appealed, but the dismissal was cemented in 2008 by an appeals court. As of 2006, the Vietnamese government estimated there were over 4,000,000 victims of dioxin poisoning in Vietnam, although the US government denies any conclusive scientific links between Agent Orange and Vietnamese victims of dioxin poisoning. In some areas of southern Vietnam, dioxin levels remain at over 100 times the accepted international standard. On 22 August 2024, the Paris Court of Appeals is expected to rule on the lawsuit filed by Tran To Nga against 14 US chemical corporations that supplied Agent Orange for the US military.

The U.S. Veterans Administration has listed prostate cancer, respiratory cancers, multiple myeloma, Diabetes mellitus type 2, B-cell lymphomas, soft-tissue sarcoma, chloracne, porphyria cutanea tarda, peripheral neuropathy as, "presumptive diseases associated with exposure to Agent Orange or other herbicides during military service." Spina bifida is the sole birth defect in children of veterans, recognized as being caused by exposure to Agent Orange.

The war has featured extensively in television, film, video games, music and literature. In Vietnam, a notable film set during Operation Linebacker II was Girl from Hanoi (1974) depicting war-time life. Another notable work was the diary of Đặng Thùy Trâm, a North Vietnamese doctor who enlisted in the Southern battlefield, and was killed aged 27 by US forces near Quảng Ngãi. Her diaries were published in Vietnam as Đặng Thùy Trâm's Diary (Last Night I Dreamed of Peace), where it became a bestseller and was made into a film Don't Burn. In Vietnam, the diary has been compared to The Diary of Anne Frank, and both are used in literary education.

One of the first major films based on the war was John Wayne's pro-war The Green Berets (1968). Further cinematic representations were released during the 1970s and 1980s, the most noteworthy examples being Michael Cimino's The Deer Hunter (1978), Francis Ford Coppola's Apocalypse Now (1979), Oliver Stone's Platoon (1986) and Stanley Kubrick's Full Metal Jacket (1987). Other films include Good Morning, Vietnam (1987), Casualties of War (1989), Born on the Fourth of July (1989), Forrest Gump (1994), We Were Soldiers (2002), and Rescue Dawn (2007).

The war influenced a generation of musicians and songwriters in Vietnam, the US, and elsewhere, both pro/anti-war and pro/anti-communist, with the Vietnam War Song Project having identified 5,000+ songs referencing the conflict. The band Country Joe and the Fish recorded The "Fish" Cheer/I-Feel-Like-I'm-Fixin'-to-Die Rag in 1965, and it became one of the most influential protest anthems.

Myths play a role in the historiography of the war, and have become part of the culture of the United States. Discussion of myth has focused on US experiences, but changing myths of war have played a role in Vietnamese and Australian historiography. Scholarship has focused on "myth-busting", attacking orthodox and revisionist schools of American historiography, and challenging myths about American society and soldiery in the war.

Kuzmarov in The Myth of the Addicted Army: Vietnam and the Modern War on Drugs challenges the popular and Hollywood narrative that US soldiers were heavy drug users, in particular the notion that the My Lai massacre was caused by drug use. According to Kuzmarov, Nixon is primarily responsible for creating the drug myth. Michael Allen in Until The Last Man Comes Home accuses Nixon of mythmaking, by exploiting the plight of the National League of POW/MIA Families to allow the government to appear caring, as the war was increasingly considered lost. Allen's analysis ties the position of potential missing Americans, or prisoners into post-war politics and presidential elections, including the Swift boat controversy.

On 25 May 2012, President Barack Obama issued a proclamation of the commemoration of the 50th Anniversary of the Vietnam War. On 10 November 2017, President Donald Trump issued an additional proclamation commemorating the 50th Anniversary of the Vietnam War.

• List of conflicts in Asia
• Soviet–Afghan War
• Third Indochina War

The references for this article are grouped in three sections.

• Citations: references for the in-line, numbered superscript references contained within the article.
• Main sources: the main works used to build the content of the article, but not referenced as in-line citations.
• Additional sources: additional works used to build the article

• A Vietnam Diary's Homecoming Video produced by the PBS Series History Detectives
• Detailed bibliography of Vietnam War
• Documents Relating to American Foreign Policy–Vietnam Archived 13 August 2012 at the Wayback Machine primary sources on U.S. involvement
• Fallout of the War from the Dean Peter Krogh Foreign Affairs Digital Archives
• Glossary of Military Terms & Slang from the Vietnam War
• Impressions of Vietnam and descriptions of the daily life of a soldier from the oral history of Elliott Gardner, U.S. Army Archived 30 April 2011 at the Wayback Machine
• Stephen H. Warner Southeast Asia Photograph Collection at Gettysburg College
• Timeline US – Vietnam (1947–2001) in Open-Content project
• The U.S. Army in Vietnam the official history of the United States Army
• The Vietnam War at The History Channel
• UC Berkeley Library Social Activism Sound Recording Project: Anti-Vietnam War Protests
• Vietnam war timeline comprehensive timeline of the Vietnam War
• Virtual Vietnam Archive – Texas Tech University
• 1965–1975 Another Vietnam; Unseen images of the war from the winning side – Mashable
• Archival collections about the Vietnam War, University Archives and Special Collections, Joseph P. Healey Library, University of Massachusetts Boston