The Serbian army, led by King Peter I and Field Marshal Radomir Putnik, fought valiantly but was ultimately overwhelmed by the Central Powers' forces.

By the end of the Serbian campaign of 1915, the Central Powers had effectively eliminated Serbia as a threat, secured their position in the region and opened up a land route to provide supplies to the embattled Ottoman Empire.

The Serbian government, along with the remnants of its army, evacuated to the Greek island of Corfu, where they regrouped and later played a crucial role in the ultimate Allied victory in the war.

Against all odds, the Serbian army, led by General Radomir Putnik managed to repel multiple offensives from a much larger and better-equipped enemy.

Russia posed a significant threat as an adversary, and the entry of Italy into the war on the side of the Allies further complicated the challenges faced by the Austro-Hungarian forces.

Following the Allied defeat in the Gallipoli campaign and the Russian setback at Gorlice, Tsar Ferdinand of Bulgaria signed a treaty with Germany and on 23 September 1915 started mobilisation for war.

Early on 7 October crossing of the Sava by Austro-Hungarian Third Army, including the German XXII Reserve Corps, began supported by monitors from the Imperial and Royal Danube Flotilla.

[28] On 8 October German troops managed to reach the south bank of the Sava, threatening the Serbian west flank and the north of Belgrade.

[26] The Bulgarian First Army first made quick progress as the Serbs had moved troops north and the border units were of "low quality" but was stopped by the Serbian Second Army which made the German general staff request reinforcements, resulting in the German Alpine Corps brought in from the French front, as well as the Austro-Hungarian 10th Mountain Brigade.

[36] After Greece chose to remain neutral, despite the terms of the treaty of alliance with Serbia, the Allies agreed to send a force to support the Serbs.

This advance provided some limited assistance to the retreating Serbian army, as the Bulgarians had to concentrate larger forces on their southern flank to deal with the threat, which led to the Battle of Krivolak.

The French and British soldiers, moving up in two columns on both sides of the Vardar River into Serbian Macedonia, comprised a total force of 60,000 men.

Facing the oncoming German III Corps, Austro-Hungarian units to the west, and the Bulgarian 9th Infantry Division blocking the southern route through Niš, the Serbian army abandoned Kragujevac without a fight.

[39] Field Marshal Mackensen ordered a pursuit by the Bulgarians southwest toward Pristina, however, the First Army encountered challenges in crossing the West and South Morava Rivers.

As the Central Powers advanced, the Serbian army managed to maintain its organisational integrity and hold off their pursuers despite the loss of key cities.

The Serbian forces reached Pristina and Kosovo ahead of their pursuers and chose to continue retreating towards Prizren, escaping the enemy's attempts to encircle them.

[42] To escape the encirclement by the Central Powers, on 25 November 1915, the government and the supreme command made the decision to withdraw across the Accursed Mountains of Montenegro and Albania.

It was a perilous journey undertaken in the midst of winter, with severe weather conditions, difficult roads, and the constant threat of attacks by enemy forces and Albanian tribal bands.

Both the Austro-Hungarian and Bulgarian occupation administrations implemented stringent measures,[46][47] subjecting the population to various forms of repression, including mass internment, forced labor, concentration camps for political opponents, famine, denationalisation, and policies aimed at cultural assimilation.