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
Serbia to become an anchor for unification of all South Slavs, and the relationship between the two countries became tense. The assassination of Archduke Franz Ferdinand of Austria on 28 June 1914 in Sarajevo by Gavrilo Princip, a member of the Young Bosnia organization, led to Austria-Hungary declaring war on Serbia. In defense of Serbia, and to maintain her status as a Great Power, Russia mobilized its troops, which resulted in Austria-Hungary's ally Germany declaring war on Russia. Serbia won the first major battles of World War I, including the Battle of Cer and Battle of Kolubara – marking the first