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
Robert, Archduke of Austria-Este assassinated relative Archduke Franz Ferdinand of Austria, (1863–1914), who had inherited in 1875 the Austria-Este designation and what had been salvaged of the Este fortune when the duchy was annexed to Italy in 1860. Archduke Robert descended through his Habsburg father from Ercole III d'Este, Duke of Modena, and his mother Zita was a descendant of Maria Beatrice d'Este, heiress of Modena and her husband, Archduke Ferdinand of Austria. Thus the lineage of the last Este dukes, in female descent, remained joined to the Austria-Este legacy. Archduke Robert eventually adopted use for himself and his descendants in male line the