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 Joseph Francis of Austria Archduke Joseph Francis of Austria Josef Franz, Archduke of Austria, Prince of Hungary (Josef Franz Leopold Anton Ignatius Maria; 28 March 1895 – 25 September 1957), was the eldest son of Archduke Joseph August of Austria and Princess Auguste Maria of Bavaria. As his father was the last Palatine of Hungary and was briefly considered a possible King of Hungary in 1919–1920, Josef Franz was a potential crown prince of Hungary. He was born during the reign of his maternal great-grandfather, Francis Joseph I of Austria, who was also his second cousin once removed on his father's side. On 4