The Assassination That Started A War
After the 1878 Treaty of Berlin, Austria-Hungary was to occupy and administer the Ottoman Vilayet of Bosnia, although the Ottoman Empire kept official sovereignty; additionally, the Principality of Serbia was officially recognized as a sovereign state. It was to become a kingdom four years later under Prince Milan IV Obrenović and maintained close relations with Austria-Hungary. However, in 1903, when the king was assassinated, Peter I of the House of Karađorđević was installed as king. The new regime, which was more nationalist, was more closely allied to Russia and less to Austria-Hungary. It also began a period when Serbia started to try to rebuild its power and reclaim its empire. The resultant Serbian military successes and outrage over the Austro-Hungarian annexation of Bosnia-Herzegovina goaded the Serbian nationalists.
Prior to 1914, lone assassins unsuccessfully tried to assassinate Austro-Hungarian officials. A collective of revolutionary groups, which came to be called Young Bosnia, formed with the goal of ending Austro-Hungarian rule in Bosnia, and unifying the Slavs in Southeastern Europe. Then, in 1911, the Black Hand was established. This secret society was dedicated to creating a Greater Serbia through “terroristic action.” Because of his political stances, and his planned reforms, Peter I was seen as a threat.