text: The Soviet Union, officially the Union of Soviet Socialist Republics (USSR, Russian: СССР), was a socialist state in Eurasia that existed from 1922 to 1991. Nominally a union of multiple equal national Soviet republics, its government and economy were highly centralized. The country was a one-party state, governed by the Communist Party with Moscow as its capital in its largest republic, the Russian Soviet Federative Socialist Republic. The Russian nation had constitutionally equal status among the many nations of the union but exerted de facto dominance in various respects. Other major urban centres were Leningrad, Kiev, Minsk, Alma-Ata and Novosibirsk. The Soviet Union was one of the five recognized nuclear weapons states and possessed the largest stockpile of weapons of mass destruction. It was a founding permanent member of the United Nations Security Council, as well as a member of the Organization for Security and Co-operation in Europe (OSCE), and the leading member of the Council for Mutual Economic Assistance (CMEA) and the Warsaw Pact. 
  
  The Soviet Union had its roots in the October Revolution of 1917, when the Bolsheviks, led by Vladimir Lenin, overthrew the Russian Provisional Government which had replaced Tsar Nicholas II during World War I. In 1922, the Soviet Union was formed with the unification of the Russian, Transcaucasian, Ukrainian, and Byelorussian republics. Following Lenin's death in 1924 and a brief power struggle, Joseph Stalin came to power in the mid-1920s. Stalin committed the state's ideology to Marxism–Leninism (which he created), and initiated a centrally planned economy which led to a period of rapid industrialization and collectivization. During this period of totalitarian rule, Stalin imposed political paranoia; the mid-1930s Great Purge removed his opponents within and outside of the party via arbitrary arrests and persecutions of many people. Suppression of political critics, forced labor, and famines were perpetrated by Stalin; in 1933, a major famine struck Soviet Ukraine, causing the deaths of over 7 million people.