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
July Crisis July Crisis The July Crisis was a series of interrelated diplomatic and military escalations among the major powers of Europe in the summer of 1914 that was the penultimate cause of World War I. The crisis began on June 28, 1914, when Gavrilo Princip, a Bosnian Serb, assassinated Archduke Franz Ferdinand, heir presumptive to the Austro-Hungarian throne. A complex web of alliances, coupled with miscalculations by many leaders that war was in their best interests or that a general war would not occur, resulted in a general outbreak of hostilities among every major European nation in early August 1914. Austria-Hungary