Franz Joseph I of Austria of his only son and heir, Crown Prince Rudolf, in 1889, and the assassination of his wife, Empress Elisabeth, in 1898. After the Austro-Prussian War, Austria-Hungary turned its attention to the Balkans, which was a hotspot of international tension because of conflicting interests with the Russian Empire. The Bosnian Crisis was a result of Franz Joseph's annexation of Bosnia and Herzegovina in 1908, which had been occupied by his troops since the Congress of Berlin (1878). On 28 June 1914, the assassination of his nephew, Archduke Franz Ferdinand, in Sarajevo resulted in Austria-Hungary's declaration of war against the Kingdom of
Assassination of Archduke Franz Ferdinand advocate of increased federalism and widely believed to favor trialism, under which Austria-Hungary would be reorganized by combining the Slavic lands within the Austro-Hungarian empire into a third crown. A Slavic kingdom could have been a bulwark against Serb irredentism, and Franz Ferdinand was therefore perceived as a threat by those same irredentists. Princip later stated to the court that preventing Franz Ferdinand's planned reforms was one of his motivations. The day of the assassination, June 28 (June 15 in the Julian calendar), is the feast of St. Vitus. In Serbia, it is called Vidovdan and commemorates the 1389 Battle