Broadly speaking, Central Serbia is the historical core of modern Serbia, which emerged from the Serbian Revolution (1804–17) and subsequent wars against the Ottoman Empire. In the following century, Serbia gradually expanded south, acquiring South Serbia, Kosovo, Sandžak and Vardar Macedonia, and in 1918 – following the unification and annexation of Montenegro and unification of Austro-Hungarian areas left of the Danube and Sava (Vojvodina) – it merged with other South Slavic territories into the Kingdom of Yugoslavia. The current borders of Central Serbia were defined after World War II, when Serbia became a republic within the Socialist Federal Republic of Yugoslavia, with Kosovo and Vojvodina as its autonomous provinces.