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
German occupation of Luxembourg during World War I neutral state. The Luxembourg Crisis had seen Prussia thwart France's attempt to purchase the Grand Duchy from the Netherlands. Luxembourg's neutrality was accepted by Prussia's then-Chancellor, Otto von Bismarck, who boasted, "In exchange for the fortress of Luxembourg, we have been compensated by the neutrality of the country, and a guarantee that it shall be maintained in perpetuity." In June 1914, Archduke Franz Ferdinand, heir to the thrones of Austria-Hungary, was assassinated by pan-Slavic nationalists, leading to a sudden deterioration in relations between Austria-Hungary and Serbia. Austria-Hungary was supported by the German Empire, while Serbia had the backing of the