Franz Joseph was troubled by nationalism during his entire reign. He concluded the Austro-Hungarian Compromise of 1867, which granted greater autonomy to Hungary and transformed the Austrian Empire into the Dual Monarchy of Austria-Hungary. He ruled peacefully for the next 45 years, but personally suffered the tragedies of the execution of his brother Emperor Maximilian I of Mexico in 1867, the suicide of his son Crown Prince Rudolf in 1889, the assassination of his wife Empress Elisabeth ("Sisi") in 1898, and the assassination of his nephew and heir-presumptive, Archduke Franz Ferdinand, in 1914. 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 Franz Ferdinand in Sarajevo resulted in Austria-Hungary's declaration of war against the Kingdom of Serbia, which was an ally of the Russian Empire. That activated a system of alliances which resulted in World War I. The Emperor died in 1916, after ruling his domains for almost 68 years. He was succeeded by his grandnephew Charles.