Trifko Grabež society. For the next two years he spent most of his spare time with other nationalists who favoured a union between Bosnia and Herzegovina and Serbia. When it was announced that Archduke Franz Ferdinand, the heir to the throne of Austro-Hungarian Empire, was going to visit Bosnia and Herzegovina in June 1914, Colonel Dragutin Dimitrijević, the chief of the Intelligence Department in the Serbian Army and head of the Black Hand, sent seven men, Grabež, Nedeljko Čabrinović, Vaso Čubrilović, Cvjetko Popović, Danilo Ilić, Muhamed Mehmedbašić and Gavrilo Princip to Sarajevo to assassinate him. Each man was given either a revolver
Serbia to become an anchor for unification of all 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 organization, led to Austria-Hungary declaring war on Serbia. In defense of Serbia, and to maintain her status as a Great Power, Russia mobilized its troops, which resulted in Austria-Hungary's ally Germany declaring war on Russia. Serbia won the first major battles of World War I, including the Battle of Cer and Battle of Kolubara – marking the first