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. Serbia's casualties accounted for 8% of the total Entente military deaths; 58% (243,600) soldiers of the Serbian army perished in the war. The total number of casualties is placed around 700,000, more than 16% of Serbia's prewar size, and a majority (57%) of its overall male population. Serbia suffered the biggest casualty rate in World War I. Kingdom of Yugoslavia The beginnings of the idea of the first common South Slavic state were the signing of a declaration on the island of Corfu in 1917. The Corfu Declaration was a formal agreement between the government-in-exile of the Kingdom of Serbia and the Yugoslav Committee (anti-Habsburg South Slav émigrés) that pledged to unify Kingdom of Serbia and Kingdom of Montenegro with Austria-Hungary’s South Slav autonomous crown lands: Kingdom of Croatia-Slavonia, Kingdom of Dalmatia, Slovenia, Vojvodina (then part of the Kingdom of Hungary) and Bosnia and Herzegovina in a post-war Yugoslav state. It was signed on 20 July 1917 on Corfu. As the Austro-Hungarian Empire collapsed, the territory of Syrmia united with Serbia on 24 November 1918. Just a day later on 25 November 1918 Grand National Assembly of Serbs, Bunjevci and other Slavs in Banat, Bačka and Baranja declared the unification of Banat, Bačka, and Baranja to the Kingdom of Serbia. On 26 November 1918, the Podgorica Assembly deposed the House of Petrović-Njegoš and united Montenegro with Serbia. On 1 December 1918, in Belgrade, Serbian Prince Regent Alexander Karađorđević proclaimed the Kingdom of the Serbs, Croats, and Slovenes, under King Peter I of Serbia. King Peter was succeeded by his son, Alexander, in August 1921. Serb centralists and Croat autonomists clashed in the parliament, and most governments were fragile and short-lived. Nikola Pašić, a conservative prime minister, headed or dominated most governments until his death. King Alexander established a dictatorship in 1929 with the aim of establishing the Yugoslav ideology and single Yugoslav nation, changed the name of the country to Yugoslavia and changed the internal divisions from the 33