The Union of Soviet Socialist Republics (Russian: Сою́з Сове́тских Социалисти́ческих Респу́блик, tr. Soyuz Sovetskikh Sotsialisticheskikh Respublik; IPA: [sɐˈjus sɐˈvʲɛtskʲɪx sətsɨəlʲɪsˈtʲitɕɪskʲɪx rʲɪˈspublʲɪk] ( listen)) abbreviated to USSR (Russian: СССР, tr. SSSR) and SU (Russian: СС, tr. SS) or shortened to the Soviet Union (Russian: Сове́тский Сою́з, tr. Sovetskij Soyuz; IPA: [sɐ'vʲetskʲɪj sɐˈjʉs]), was a Marxist–Leninist state on the Eurasian continent that existed between 1922 and 1991. It was governed as a single-party state by the Communist Party with Moscow as its capital. A union of multiple subnational Soviet republics, its government and economy were highly centralized.

The Soviet Union had its roots in the Russian Revolution of 1917, which overthrew the Russian Empire. The Bolsheviks, the majority faction of the Social Democratic Labour Party, led by Vladimir Lenin, then led a second revolution which overthrew the provisional government and established the Russian Socialist Federative Soviet Republic (renamed Russian Soviet Federative Socialist Republic in 1936), beginning a civil war between pro-revolution Reds and counter-revolution Whites. The Red Army entered several territories of the former Russian Empire, and helped local Communists take power through soviets that nominally acted on behalf of workers and peasants. In 1922, the Communists were victorious, forming the Soviet Union with the unification of the Russian, Transcaucasian, Ukrainian, and Byelorussian republics. Following Lenin's death in 1924, a troika collective leadership and a brief power struggle, Joseph Stalin came to power in the mid-1920s. Stalin suppressed political opposition to him, committed the state ideology to Marxism–Leninism (which he created) and initiated a centrally planned economy. As a result, the country underwent a period of rapid industrialisation and collectivisation which laid the basis for its later war effort and dominance after World War II. However, Stalin established political paranoia, and introduced arbitrary arrests on a massive scale after which the authorities transferred many people (military leaders, Communist Party members, ordinary citizens alike) to correctional labour camps or sentenced them to execution.