The Union of Soviet Socialist Republics (abbreviated to USSR (Russian: СССР) or shortened to the Soviet Union, was a Marxist–Leninist state on the Eurasian continent that existed between 1922 and 1991. A union of multiple sub-national Soviet republics, its government and economy were highly centralized. The Soviet Union was a single-party state, governed by the Communist Party with Moscow as its capital.
The Soviet Union had its roots in 1917 when the Bolsheviks, headed by Vladimir Lenin, led the October Revolution which overthrew the provisional government that had replaced the Tsar. They 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, which 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.