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
Archduke Franz Ferdinand of Austria themselves after him. Archduke Franz Ferdinand of Austria Archduke Franz Ferdinand, Archduke of Austria-Este (Franz Ferdinand Carl Ludwig Joseph Maria; 18 December 1863 – 28 June 1914) was a member of the imperial Habsburg dynasty, and from 1896 until his death the heir presumptive ("Thronfolger") to the Austro-Hungarian throne. His assassination in Sarajevo precipitated Austria-Hungary's declaration of war against Serbia, which in turn triggered a series of events that resulted in Austria-Hungary's allies and Serbia's declaring war on each other, starting World War I. Franz Ferdinand was born in Graz, Austria, the eldest son of Archduke Karl Ludwig of Austria