Battle of Kolubara their respective commands, and the 5th and 6th armies were merged into a single 5th Army of 95,000 men. On 28 June 1914, Bosnian Serb student Gavrilo Princip assassinated Archduke Franz Ferdinand of Austria in Sarajevo. The assassination precipitated the July Crisis, which led Austria-Hungary to issue an ultimatum to Serbia on 23 July on suspicion that the assassination had been planned in Belgrade. The Austro-Hungarian government made the ultimatum intentionally unacceptable to Serbia, and it was indeed rejected. The Austro-Hungarians declared war on Serbia on 28 July and that same day the Serbs destroyed all bridges on the Sava
Serbian nationalism some Štokavian-speaking peoples to call themselves names other than Serbs. Ilija Garašanin was another early proponent of Serbian nationalism and a proponent of a Greater Serbia - a Serbian state whose borders were extended to include all Serbs in the Balkan region. After Serbia was recognized as an independent state in 1878, both South Slavs and the Serbian government considered their peoples in Habsburg-ruled Austria-Hungary to be under occupation resulting in increasing antagonism between Serbia and Austria-Hungary from the late 19th century to the early 20th century. In 1914 Austrian Archduke Franz Ferdinand was assassinated by Bosnian Serb revolutionary Gavrilo