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 Serbs 1914, a young Bosnian Serb student named Gavrilo Princip assassinated Archduke Franz Ferdinand of Austria, which directly contributed to the outbreak of World War I. In the fighting that ensued, Serbia was invaded by Austria-Hungary. Despite being outnumbered, the Serbs subsequently defeated the Austro-Hungarians at the Battle of Cer, which marked the first Allied victory over the Central Powers in the war. Further victories at the battles of Kolubara and the Drina meant that Serbia remained unconquered as the war entered its second year. However, an invasion by the forces of Germany, Austria-Hungary and Bulgaria overwhelmed the Serbs in the