The ethnicities that made up Yugoslavia had very separate pasts, much of which can be attributed to the fact that the region found itself at the fault line of several empires. Serbs are considered to be a purely Slavic people, who came to Europe in the 4th Century with the Huns, and later fell under Byzantine rule around 850. In the 13th Century, after fighting for independence from the empire, the Kingdom of Serbia was recognized in 1218. In 1389, the Serbs were defeated by the Turks in the Battle of Kosovo. This moment is idealized by many even to this day to remind Serbs of their nationhood. Turkish influence declined over the following centuries until they were defeated in 1877. This new independence was short lived, and Austro-Hungarian influence took over in 1880.

    The turning point of the region's domination by empires began with the Balkan Wars in 1912. Serbia, Bulgaria, and Greece allied with Montenegro to battle the Ottomans. As the region settled, the Serbs came out with large new tracts of land and power, while Bulgaria was unsatisfied with the divison of Macedonia that was laid out in 1913. With backing from Autria-Hungary, Bulgaria went to war with Serbia, initiating the Second Balkan War in June of 1913. Serbia again came out victorious and gained more land, but also more enemies. The volatile region saw even more fighting as Archduke Ferdinand was assassinated in 1914. As the heir to the Hapsburg throne, his murder led to an ultimatum being handed down to Serbia, who declined to allow Austro-Hungarian influence in its investigation of the crime. War was declared, and the system of alliances in Europe meant that more and more nations were drawn into the conflict and World War I began.

    The fighting of WWI left the region decimated. Serbia lost approximately ¼ of its prewar population, and ½ of its resources. Montenegro also saw ¼ of its population die, and Croats and Slovenes felt heavy loses as well. Nevertheless, the war ended as the Austro-Hungarian Empire collapsed in November of 1918.

    Towards the end of the war, the people of the Balkans decided to band together to defend themselves against a feared attack by Italy, who had been promised lands in the region in 1915 by the Entente forces. In July of 1917, the Corfu Agreement was signed. This document described a union of the Croats, Serbs, and Slovenes under one government. source