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. Thus neutral Greece found itself increasingly
drawn into the war. Pursuing the retreating Serbs, the Central Powers also
occupied Albania, while
defeat of Montenegro followed in January 1916. 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. Entente offensives on the Macedonian Front were ineffective until September 1918, when the
Vardar offensive abruptly overcame Bulgarian and Central Powers defenses beginning with the
Battle of Dobro Pole on 15 September. In late September, mutiny struck the Bulgarian army, whose will to fight was exhausted. Entente forces advanced quickly into
Vardar Macedonia. On 29 September, Serbian and French forces liberated
Skopje, then known as Uskub, as
Bulgaria capitulated. The Bulgarian armistice allowed the Entente unopposed access to Bulgarian railways and required Bulgaria to expel other Central Powers forces. This drove a decisive Central Powers collapse on all fronts and an unexpectedly quick end to the wider war. Greatly outnumbered and exposed, German and Austro-Hungarian forces in the Balkans, including the
11th Army in Serbia, the XIX Corps in Albania, and small units supporting Bulgaria, fled northward toward Hungary in defeat or forced withdrawal. With no Central Powers forces remaining between Greek and British forces and
Constantinople, the Ottoman Empire concluded an
armistice on 30 October. Liberation of Belgrade on 1 November, threatening almost unopposed Serbian and French invasion of Hungary, combined with domestic ethnic revolts and growing military mutiny, helped force Austria-Hungary to an
armistice on 3 November. On 10 November,
Romania repudiated the
Treaty of Bucharest and re-entered the war. Alone and facing imminent, certain defeat, Germany agreed to
armistice on 11 November. == Liberation of Serbia, Albania and Montenegro ==