1878, which ended the Russo-Turkish War; this treaty, however, prohibited Serbia from uniting with other Serbian regions by placing Bosnia and Herzegovina under Austro-Hungarian occupation, alongside the occupation of the region of Raška. From 1815 to 1903, the Principality of Serbia was ruled by the House of Obrenović, save for the rule of Prince Aleksandar Karađorđević between 1842 and 1858. In 1882, Principality of Serbia became the Kingdom of Serbia, ruled by King Milan I. The House of Karađorđević, descendants of the revolutionary leader Karađorđe Petrović, assumed power in 1903 following the May Overthrow. In the north, the 1848 revolution in Austria led to the establishment of the autonomous territory of Serbian Vojvodina; by 1849, the region was transformed into the Voivodeship of Serbia and Banat of Temeschwar. The Balkan Wars and World War I In the course of the First Balkan War in 1912, the Balkan League defeated the Ottoman Empire and captured its European territories, which enabled territorial expansion of the Kingdom of Serbia into regions of Raška, Kosovo, Metohija, and Vardarian Macedonia. The Second Balkan War soon ensued when Bulgaria turned on its former allies, but was defeated, resulting in the Treaty of Bucharest. In two years, Serbia enlarged its territory by 80% and its population by 50%, it also suffered high casualties on the eve of World War I, with more than 36,000 dead. Austria-Hungary became wary of the rising regional power on its borders and its potential to become an anchor for unification of Serbs and other South Slavs, and the relationship between the two countries became tense. The assassination of Archduke Franz Ferdinand of Austria on 28 June 1914 in Sarajevo by Gavrilo Princip, a member of the Young Bosnia organisation, led to Austria-Hungary declaring war on Serbia, on 28 July 1914. Local war escalated when Germany declared war on Russia and invaded France and Belgium, thus drawing Great Britain into the conflict that became the First World War. Serbia won the first major battles of World War I, including the Battle of Cer, and the Battle of Kolubara, marking the first Allied victories against the Central Powers in World War I. 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