The Soviet Union, officially the Union of Soviet Socialist Republics, was a socialist state that spanned Europe and Asia during its existence from 1922 to 1991. It was nominally a federal union of multiple national republics; in practice its government and economy were highly centralized until its final years. The country was a one-party state prior to 1990 governed by the Communist Party of the Soviet Union, with Moscow as its capital within its largest and most populous republic, the Russian SFSR. Other major urban centers were Leningrad, Kiev, Minsk, Tashkent, Alma-Ata and Novosibirsk. It was the largest country in the world, covering over 22,402,200 square kilometres, and spanning eleven time zones.
The Soviet Union had its roots in the October Revolution of 1917 when the Bolsheviks, headed by Vladimir Lenin, overthrew the Provisional Government that had earlier replaced the monarchy of the Russian Empire.