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 of Franz Joseph and Maximilian) and of his second wife, Princess Maria Annunciata of Bourbon-Two Sicilies. In 1875, when he was only eleven years old, his cousin Francis V, Duke of Modena died, naming Franz Ferdinand his heir on condition that he add the name "Este" to his own. Franz Ferdinand thus became one of the wealthiest men in Austria. In 1889, Franz Ferdinand's life changed dramatically. His cousin Crown Prince Rudolf committed suicide at his hunting lodge in Mayerling. This left Franz Ferdinand's father, Karl Ludwig, as first in line to the throne. Karl Ludwig died of typhoid fever