The Balkan Peninsula, a region of Southeastern Europe, has been the source of numerous conflicts throughout the 20th century. In the 1990s, the Bosnian War was a major international crisis in the wake of the break up of Yugoslavia. In the summer of 1914, Austria declared war against Serbia following the assassination of Archduke Franz Ferdinand in Sarajevo, initiating World War I. Previous to that, there were two wars, the Balkan Wars, in 1912 and 1913, that set the stage for the larger, global conflict.
In the later decades of the 19th century, several nations in the Balkans declared their independence from the Ottoman Empire. These nations included Greece, Bulgaria, and Serbia. In 1912 these nations, along with Montenegro, formed the Balkan League. Later that year, on 8 October, the Balkan League attacked the Ottoman Empire. Seven months of fighting ended with the Treaty of London (30 May 1913) and the loss of all Balkan territory of the part of the Ottoman Empire.
The Second Balkan War broke out on 16 June 1913, when Bulgaria, attacked its former allies. Both Romania and the Ottoman Empire entered the conflict, resulting in a quick and decisive defeat of Bulgaria and the loss of much of the territory it had gained as a result of the First Balkan War. The numerous conflicts in the former nation of Yugoslavia, lasting from 1991 to 2001, are often referred to as the Third Balkan War.