Serbian Campaign of World War I Serbia, Montenegro, and Greece. When Bulgaria attacked both Serbia and Greece on 16 June 1913, it lost most of its Macedonian region to those countries, and additionally the Southern Dobruja region to Romania and Adrianople (the present-day city of Edirne) to Turkey in the 33-day Second Balkan War, which further destabilized the region. On 28 June 1914, Gavrilo Princip, a Bosnian Serb student and member of a multi-ethnic organisation of national revolutionaries called Young Bosnia, assassinated Archduke Franz Ferdinand of Austria, the heir to the Austro-Hungarian throne, in Sarajevo, Bosnia. The political objective of the assassination was the independence of
Austria–Russia relations Treaty of Berlin. While Russia eventually backed down, relations between the two Empires were permanently damaged. The lasting result was bitter enmity between Austria-Hungary on one side and Serbia and Russia on the other. Following the assassination of Archduke Franz Ferdinand of Austria by Serb nationalists of the Black Hand secret society on 28 June 1914, Austria delivered the July Ultimatum to Serbia demanding that the Austrian police and military have the right to enter Serbia. Serbia rejected the ultimatum and on 28 July 1914, Austria-Hungary declared war on Serbia. On August 6, the Emperor Franz Joseph signed the Austro-Hungarian