The League of Communists of Yugoslavia, known until 1952 as the Communist Party of Yugoslavia, was the founding and ruling party of SFR Yugoslavia. It was formed in 1919 as the main communist opposition party in the Kingdom of Serbs, Croats and Slovenes and after its initial successes in the elections, it was proscribed by the royal government and was at times harshly and violently suppressed. It remained an illegal underground group until World War II when, after the invasion of Yugoslavia in 1941, the military arm of the party, the Yugoslav Partisans, became embroiled in a bloody civil war and defeated the Axis powers and their local auxiliaries. After the liberation from foreign occupation in 1945, the party consolidated its power and established a one-party state, which existed until 1990, two years prior to the breakup of Yugoslavia. The party, which was led by Josip Broz Tito from 1937 to 1980, was the first communist party in power in the history of the Eastern Bloc that openly opposed the Soviet Union and thus was expelled from the Cominform in 1948 in what is known as the Tito–Stalin split. After internal purges of pro-Soviet members, the party renamed itself the League of Communists in 1952 and adopted the politics of workers' self-management and an independent path to communism, known as Titoism. Opposition party Establishment The Kingdom of Serbs, Croats and Slovenes (later renamed Yugoslavia) was established in late 1918 at the end of the World War I. Socialist movement in the territory of the new state reflected political divisions existing before the war. For example, in what was then Austria-Hungary, the Social Democratic Party of Croatia and Slavonia (SDPCS) came into existence in 1894, two years before the Yugoslav Social-Democratic Party (, JSDS) was set up in Slovene lands. The Serbian Social Democratic Party (SSDP) was founded in 1903. In Bosnia and Herzegovina, the Social Democratic Party of Bosnia and Herzegovina (SDPBH) was established in 1909. The SSDP deemed it natural to serve, as the largest social-democratic party in the new state, to unify like-minded political groups in the country. The SDPBH formally proposed a merger of such parties, but the SDPCS, the JSDS, and Serbian–Bunjevac social-democrats from Vojvodina declined. In turn, only the SSDP and the SDPBH formally agreed to a merger by January 1919. A minority group on the left wing of the SDPCS split from the party