Slavonic, became the main and official language of the empire in 864. Bulgaria was instrumental in the spread of Slavic literacy and Christianity to the rest of the Slavic world. The expansion of the Magyars into the Carpathian Basin and the Germanization of Austria gradually separated the South Slavs from the West and East Slavs. Later Slavic states, which formed in the following centuries, included the Kievan Rus', the Second Bulgarian Empire, the Kingdom of Poland, Duchy of Bohemia, the Kingdom of Croatia, Banate of Bosnia and the Serbian Empire. Modern era Pan-Slavism, a movement which came into prominence in the mid-19th century, emphasized the common heritage and unity of all the Slavic peoples. The main focus was in the Balkans where the South Slavs had been ruled for centuries by other empires: the Byzantine Empire, Austria-Hungary, the Ottoman Empire, and Venice. Austro-Hungary envisioned its own political concept of Austro-Slavism, in opposition of Pan-Slavism that was predominantly led by the Russian Empire. As of 1878, there were only three majority Slavic states in the world: the Russian Empire, Principality of Serbia and Principality of Montenegro. Bulgaria was effectively independent but was de jure vassal to the Ottoman Empire until official independence was declared in 1908. The Slavic peoples who were, for the most part, denied a voice in the affairs of the Austro-Hungarian Empire, were calling for national self-determination. During World War I, representatives of the Czechs, Slovaks, Poles, Serbs, Croats, and Slovenes set up organizations in the Allied countries to gain sympathy and recognition. In 1918, after World War I ended, the Slavs established such independent states as Czechoslovakia, the Second Polish Republic, and the Kingdom of Serbs, Croats and Slovenes. One of Hitler's ambitions at the start of World War II was to exterminate, expel, or enslave most or all East and West Slavs from their native lands, so as to make living space for German settlers. This plan of genocide was to be carried into effect gradually over 25 to 30 years. The first half of the 20th century in Russia and the Soviet Union was marked by a succession of wars, famines and other disasters, each accompanied by large-scale population losses. Stephen J. Lee estimates that, by the end of World War II in 1945, the Russian population was about 90 million fewer than it could have been otherwise. Former Soviet states in Central Asia such