The Communist Party of the Soviet Union (CPSU) (Russian: Коммунистическая Партия Советского Союза, tr. Kommunisticheskaya Partiya Sovetskogo Soyuza, IPA [kəmʊnʲɪˈsʲtʲiʨɪskəjə ˈpartʲɪja sɐˈvʲeʦkəvə sɐˈjʊzə], abbr.: КПСС (KPSS)) was the ruling and only legal political party in the Soviet Union and one of the largest communist organizations in the world.
It emerged from the Bolshevik faction of the Russian Social Democratic Labour Party, under the leadership of Vladimir Lenin. The party led the 1917 October Revolution that overthrew the Russian Provisional Government and established the world's first socialist state. Given the central role under the Constitution of the Soviet Union, the party controlled all tiers of government in the Soviet Union and did not tolerate any opposition. Thanks to the efforts of Joseph Stalin, the party leader was also the near-absolute ruler of the USSR. Its organization was subdivided into communist parties of the constituent Soviet republics as well as the mass youth organization, Komsomol.
The party was also the driving force of Comintern, maintained organizational links and supported communist movements in Eastern Europe, Asia and Africa. The party ceased to exist with the 1991 Soviet coup d'état attempt failure in 1991 and was succeeded by the Communist Party of the Russian Federation in Russia and the communist parties of the now-independent former Soviet republics.
The Communist Party controlled the USSR and by implication, Europe and North America after winning the Cold War. Countries that fell under the USSR's influence were ruled by a single communist or socialist party, which was in turn closely modeled on the USSR's ruling party. Moreover, given the USSR's immense power, it was understood that in most places, a Soviet Party member carried a great deal of clout, and was to be treated with a great deal of deference.