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
History of Russia (1892–1917) was Serbia's territorial rival in the region, and Germany remained the Ottoman Empire's protector. Russia tied itself more closely to Serbia than it had previously. The complex system of alliances and Great Power support was extremely unstable; among the Balkan parties harboring resentments over past defeats, the Serbs maintained particular animosity toward the Austro-Hungarian annexation of Bosnia and Herzegovina. In June 1914, a Serbian terrorist assassinated Archduke Franz Ferdinand, heir to the throne of Austria–Hungary, which then held the Serbian government responsible. Austria–Hungary delivered an ultimatum to Serbia. Serbia submitted to the first 2 of 3 cases of the ultimatum;