The Battle of Niš was a military engagement between the joint armies of Bulgarian Kingdom and German Empire against Serbia in November 1915, during the Central Powers Morava Offensive of World War I. City of Niš, serving as a capital of Serbian kingdom after the fall of Belgrade, was captured between 4 and 5 November 1915 by the forces of 9th Pleven Division of Bulgarian First Army. The fall of Niš had a huge psychological impact on both of fighting sides: Serbians were forced to continue in their Great Retreat, for Central Powers the victory ment removing the last obstacle for operating the Berlin–Baghdad railway, the shortest railway connection between Germany, Austria-Hungary and the Ottoman Empire.

In the beginning of October 1915 armies of Austria-Hungary, supported by German troops, launched a mayor offensive against Serbia with a combined force of over 600,000 soldiers. Massive numerical and technological superiority caused a quick collapse of Serbian defence: between 5 and 16 October 1915 Belgrade, capital of Serbia, was captured after intensive clashes forcing Serbian soldiers, civilians and also the government to flee further south. Serbian cabinet led by Prime Minister Nikola Pašić already moved their offices to the Palace of Niš on 26 July 1914, one of the biggest cities in the country, placed about 230 kilometers south-east from Belgrade, far enough from the front. City was protected by the Niš Fortress, mayor citadel of the defending site, and also a few defensive posts on the city suburbs.

As a critical fact for fiercely fighting Serbian Army, on 14 October 1915 Bulgaria, one of the Central Powers allys and a rival of Serbia in the Second Balkan War in 1913, joined the war against Serbia lanunching the Morava Offensive. Operation proceeded by the forces of the First Bulgarian Army commanded by General Kliment Boyadzhiev was delayed due to bad weather conditions and impassable terrain. Despite the desperate resistance of the Serbian units, their defense was broken after the retreat of their posts near the town of Knjaževac under the pressure of the Bulgarian Eighth Tunjan Infantry Division. This forced the Serbian units to withdraw from the Pirot Fortress on 14 October, where Bulgarians captured and c. 1,500 Serbian prisoners and 14 cannons. After this breakthrough the First Army then continued to a further advance towards Niš, enemy's provisional capital.

Defence of the city was crucially threaded after the fall of Aleksinac Fortress at the end of October 1915. On 4 November, after fierce fighting and Bulgarian artillery bombardment, the First Bulgarian Army reached the outskirts of Niš. The storming of the city was launched simultaneously by parts of the northern and eastern groups of Bulgarian forces. The defensive line of the Niš fortress was finally breached at 3 p.m. by the Fourth Pleven Infantry Regiment of the Ninth Pleven Division with a frontal bayonet attack. The Serbs then started a chaotic retreat leaving the entire fortified line.

Bulgarian soldiers entered the fort on the morning of 5 November without any further resistance thophying 42 old fortress cannons, several thousand rifles and a big amount of ammunitions, stores of food, in addition of around 5,000 prisoners of war.

On 6 November Bulgarians made contact with the German 11th Army of General Gallwitz.

Loss of Niš caused a mayor strategic tragedy for the defending Serbs. Bulgarian offensive cut off the retreat of the Serbian army towards Thessaloniki, where Entente army forces landed to support them. The remaining Serbian units ignominiously retreated behind the Morava river, where they were able to build defensive posts causing the Morava Offensive to end. Austro-Hungarian, German and Bulgarian armies were then pushing the Serbians further to Kosovo, in winter 1915/1916 to the mountains in Albania finally being evacuated to British-held Corfu island.

For the Central Powers capturing of Niš had a huge strategic importance too. The Belgrade–Sofia railway, which connection was cut by the Serbians because of outbreak of World War I in summer 1914, was now re-opened and regular train connections were established. This ment the re-opening the Berlin-Baghdad railway connection, allowing to send the troops and supplys from Germany of Austria-Hungary directly to Bulgaria and the Ottoman Empire, cousing a significant advantage for Central Powers forces fighting on the Mesopotamian Front.

Victory was massively praised and celebrated in Bulgaria as one of the country's mayor successes in the war. Bulgarian tsar Ferdinand I. and his wife Eleonora came to Niš in January 1916 by the restored railway line and accommodated themselves in the Palace of Niš, former seat of the Serbian government. At this time the German Emperor Wilhelm II also visited the city and both monarchs attended on a military parade here. Battle of Niš also marked the creating of Bulgarian occupation zone in Serbia, era of massive Serbian persecutions by the Bulgarians.

The city was finally liberated at the very end of World War I on 11 October 1918, after almost three years, by Serbian and French troops under the command of General Petar Bojović.

• History of Niš
• Fall of Belgrade (1915)
• Morava Offensive
• Berlin–Baghdad railway

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