The Liberation of Serbia, Albania and Montenegro was a military action in the Balkans in the final weeks of World War I.

After remarkable defensive success against Austria-Hungary in 1914, Serbia was quickly defeated by combined Central Powers forces after Bulgaria declared war in October 1915.

Remnants of the Royal Serbian Army retreated to the Italian-occupied Albanian ports of Durazzo and Valona where Entente naval forces performed a sea evacuation, initially mainly to the Greek Ionian island of Corfu.

Also in October 1915, advance elements of a French and British expeditionary force arrived by sea at Salonika in Greek Macedonia.

The Central Powers thus occupied Serbia, Montenegro, and most of Albania including Durazzo, while the Entente retained Valona and occupied a portion of northern Greece, establishing the Macedonian front at Salonika to stimulate active Greek participation, to provide a place to redeploy and supply a re-organized and re-equipped Serbian army, and to fight the Central Powers in the Balkans.

This drove a decisive Central Powers collapse on all fronts and an unexpectedly quick end to the wider war.

In the center, the 1st Serbian Army under Petar Bojović and part of the French Armée d'Orient under Paul Prosper Henrys advanced north.

Here, the Serbian Army halted, as the State of Slovenes, Croats and Serbs, was proclaimed on 29 October 1918 amid the imminent collapse of Austria-Hungary.

Their advance motivated Romania to reenter the war on 10 November, as this army crossed the Danube at Svishtov, Giurgiu and Nikopol.