Despite initial success, it was eventually overpowered by the Central Powers in 1915 and Austro-Hungarian occupation of Serbia followed. Most of its army and some people retreated through Albania to Greece and Corfu, suffering immense losses on the way. Serbia was occupied by the Central Powers. After the Central Powers military situation on other fronts worsened, the remains of the Serb army returned east and led a final breakthrough through enemy lines on 15 September 1918, liberating Serbia and defeating Bulgaria and Austria-Hungary. Serbia, with its campaign, was a major Balkan Entente Power which contributed significantly to the Allied victory in the Balkans in November 1918, especially by helping France force Bulgaria's capitulation.