Yugoslavia was an artificial creation of the Allies after WW1. Effectively, Yugoslavia was in reality an extended Serbia. The King of Serbia became the King of Yugoslavia, and the Balkan states that had been part of the Hapsburg Empire, Slavonia, Slovenia, Croatia and Bosnia Herzogovina were simply annexed by Yugoslavia, against those peoples' wills. Similarly, Serbia seized and annexed Montenegro, exiling its King, who sought help from the Allies. The Allies, however, allowed Serbia's fait accompli to stand. The Yugoslav Parliament was dominated by Serbia, so the perception in Croatia, for example, that the other Balkan states were merely Serbian possessions rather than equal regions of Yugoslavia with equal status. With the German and Italian invasion of 1941, the "satellite" states sided with the Germans and Italians to free themselves from Serb domination. There was a vicious war within Yugoslavia between the Royalist Serb forces, the Cetniks, the Communist backed Partisans, led by Tito, and the Croat paramilitaries, the Ustase, which the Partisans ultimately won. Hence, Yugoslavia emerged from the war as a strongly centralised communist state with Tito (ethnically a Croat) firmly in control. He was able to play off the Russians against the West very effectively, allowing Yugoslavia to develop economically and culturally far more than the rest of the Russian satellite states. That Tito liberated Yugoslavia from the Axis forces without significant Soviet help enabled him to do this effectively. No Soviet garrison was ever allowed, which enabled Tito to build a personal dictatorship with a communist facade. On Tito's death, however, the power vacuum often caused by the death of a paternalistic dictator, led to the non-Serb states seeking autonomy. The Serb dominated government refused to allow this, so independence movements developed, and became increasingly militant until violence broke out leading to what tends to be referred to as the Yugoslav Civil War, resulting in the fragmentation of Yugoslavia, amidst terrible human suffering.