The Union of Soviet Socialist Republics (USSR), commonly known as the Soviet Union, was a transcontinental country that spanned much of Eurasia from 1922 to 1991. It was the largest country in the world by area, extending across eleven time zones and sharing land borders with twelve countries. A successor state to the Russian Empire, the country was nominally organized as a federal union of fifteen national republics, the largest and most populous of which was the Russian SFSR; in practice both its government and economy were highly centralized until its final years. It was the world's third-most populous country and Europe's most populous country. As a one-party state governed by the Communist Party of the Soviet Union, it was a flagship communist state. Its capital as well its largest city was Moscow. Other highly urbanized centers were Leningrad, Kiev, Tashkent and Baku.

The Russian Soviet Federative Socialist Republic, previously known as the Russian Soviet Republic and the Russian Socialist Federative Soviet Republic, as well as being unofficially referred to as Soviet Russia, the Russian Federation, or simply Russia, was an independent federal socialist state from 1917 to 1922, and afterwards the largest and most populous constituent republic of the Soviet Union (USSR) from 1922 to 1991, until becoming a sovereign part of the Soviet Union with priority of Russian laws over Union-level legislation in 1990 and 1991, the last two years of the existence of the USSR. The Russian SFSR was composed of sixteen smaller constituent units of autonomous republics, five autonomous oblasts, ten autonomous okrugs, six krais and forty oblasts. Russians formed the largest ethnic group. The capital of the Russian SFSR and the USSR as a whole was Moscow and the other major urban centers included Leningrad, Stalingrad, Novosibirsk, Sverdlovsk, Gorky and Kuybyshev. It was the first socialist state in the world.