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
Assassination of Archduke Franz Ferdinand advocate of increased federalism and widely believed to favor trialism, under which Austria-Hungary would be reorganized by combining the Slavic lands within the Austro-Hungarian empire into a third crown. A Slavic kingdom could have been a bulwark against Serb irredentism, and Franz Ferdinand was therefore perceived as a threat by those same irredentists. Princip later stated to the court that preventing Franz Ferdinand's planned reforms was one of his motivations. The day of the assassination, June 28 (June 15 in the Julian calendar), is the feast of St. Vitus. In Serbia, it is called Vidovdan and commemorates the 1389 Battle