The Soviet Union, officially the Union of Soviet Socialist Republics, also known unofficially as Russia, was a federal socialist state in Eurasia that existed from 1922 to 1991. Nominally a union of multiple 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 and the leading member of the Council for Mutual Economic Assistance and the Warsaw Pact.