The Union of Soviet Socialist Republics (Russian: Сою́з Сове́тских Социалисти́ческих Респу́блик, tr. Soyuz Sovetskikh Sotsialisticheskikh Respublik) abbreviated to USSR (Russian: СССР, tr. USSR) or the Soviet Union (Russian: Советский Союз, tr. Sovetsky Soyuz), was a constitutionally socialist state that existed between 1922 and 1991, ruled as a single-party state by the Communist Party with its capital as Moscow. A union of 15 sub national Soviet republics, its government and economy were highly centralized.