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
History of the Balkans war set the stage for the Balkan crisis of 1914 and thus was a "prelude to the First World War." The monumentally colossal World War I was ignited from a spark in the Balkans, when a Bosnian Serb named Gavrilo Princip assassinated the heir to the Austrian throne, Franz Ferdinand. Princip was a member of a Serbian militant group called the Crna Ruka (Serbian for "Black Hand"). Following the assassination, Austria-Hungary sent Serbia an ultimatum in July 1914 with several provisions largely designed to prevent Serbian compliance. When Serbia only partially fulfilled the terms of the ultimatum, Austria-Hungary declared war