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
Austria–Russia relations Treaty of Berlin. While Russia eventually backed down, relations between the two Empires were permanently damaged. The lasting result was bitter enmity between Austria-Hungary on one side and Serbia and Russia on the other. Following the assassination of Archduke Franz Ferdinand of Austria by Serb nationalists of the Black Hand secret society on 28 June 1914, Austria delivered the July Ultimatum to Serbia demanding that the Austrian police and military have the right to enter Serbia. Serbia rejected the ultimatum and on 28 July 1914, Austria-Hungary declared war on Serbia. On August 6, the Emperor Franz Joseph signed the Austro-Hungarian