The Soviet Union, formally the Union of Soviet Socialist Republics (USSR), was a socialist nation that spanned Europe and Asia throughout its existence from 1922 to 1991. It was the world's largest socialist state at the time of its dissolution. The Soviet Union was officially a federal union of numerous national republics; but, in reality, its administration and economy were heavily centralised until the last years of the Soviet Union's existence. Prior to 1990, the nation was a one-party state controlled by the Communist Party of the Soviet Union, with Moscow serving as its capital inside the Russian Soviet Socialist Republic, which was the country's biggest and most populous republic. Other significant urban centres were Leningrad (Russian Soviet Socialist Republic), Kiev (Ukrainian Soviet Republic), Minsk (Byelorussian Soviet Republic), Tashkent (Uzbek SSR), Alma-Ata (Kazakh SSR), and Novosibirsk (Russian Soviet Socialist Republic) (Russian SFSR). It was the world's biggest nation, with an area of about 22,402,200 square kilometres (8,649,500 square miles) and a time zone spread of eleven hours and forty minutes.
When the Bolsheviks led by Vladimir Lenin toppled the Provisional Government that had previously supplanted the monarchy of the Russian Empire, the Soviet Union was born. The October Revolution of 1917 was the spark that ignited the Soviet Union. They founded the Russian Soviet Republic, which was the world's first socialist state to be protected by a constitutional framework. Conflict between the Bolshevik Red Army and numerous anti-Bolshevik groups throughout the former Soviet Union, with the White Guard being the biggest part, erupted into a civil war in the summer of 1917. It was known as the White Terror because the White Guard engaged in brutal anti-communist persecution against the Bolsheviks as well as suspected worker and peasant Bolsheviks throughout the period of the revolution. It extended and assisted Bolsheviks in gaining control in their respective areas, forming soviets and repressing their political opponents and rebellious peasants via the Red Terror campaign. By 1922, the balance of power had changed, and the Bolsheviks had emerged triumphant, resulting in the union of the Russian, Transcaucasian, Ukrainian, and Byelorussian republics, which resulted in the formation of the Soviet Union. Once World War I ended, Lenin's government instituted The New Economic Policy (NEP), which resulted in the partial restoration of the free market and private property, resulting in an extended period of economic recovery.
In the four decades after Global War II, the Soviet Union coexisted as a world superpower alongside the United States, and this continued until the Soviet Union's collapse. It exerted hegemony in Eastern Europe and across the globe via military and economic power, proxy wars and influence in emerging nations, and financing of scientific research, particularly in space technology and weapons. It was also called as the "Soviet Empire."