The Kingdom of Yugoslavia (Kraljevina Jugoslavija, , "Kingdom of South Slavia) was a state in Southeast Europe and Central Europe, that existed during the interwar period (1918–1939) and first half of World War II (1939–1943). It was formed in 1918 by the merger of the provisional State of Slovenes, Croats and Serbs (itself formed from territories of the former Austro-Hungarian Empire) with the formerly independent Kingdom of Serbia. The Kingdom of Montenegro had united with Serbia five days previously, while the regions of Kosovo, Vojvodina and Vardar Macedonia were parts of Serbia prior to the unification. For its first eleven years of existence, the Kingdom was officially called the Kingdom of Serbs, Croats and Slovenes, but the term "Yugoslavia" was its colloquial name from its origins. The official name of the state was changed to "Kingdom of Yugoslavia" by King Alexander I on 3 October 1929.