Greater Serbia the Kingdom of Serbia retreated from Durrës in April 1913 under pressure of the naval fleet of Great Powers, but it remained in other parts of Albania for the next two months. The secret military society called Unity or Death, popularly known as the Black Hand, headed by Serbian colonel Dragutin Dimitrijević Apis, which took an active and militant stance on the issue of a Greater Serbian state. This organization is believed to have been responsible for numerous atrocities following the Balkan Wars in 1913. In 1914, Young Bosnia member Gavrilo Princip assassinated Archduke Franz Ferdinand in Sarajevo, which set
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