The Union of Soviet Socialist Republics (USSR), also known as the Soviet Union, was a transcontinental country that spanned much of Eurasia from 1922 until its dissolution in 1991. It was the world's third-most populous country, largest by area, and bordered twelve countries. A diverse multinational state, it was organized as a federal union of national republics, the largest and most populous being the Russian Soviet Federative Socialist Republic. In practice, its government and economy were highly centralized. As a one-party state governed by its Communist Party, it was the flagship communist state. Its capital and largest city was Moscow.
The Soviet Union's roots lay in the October Revolution of 1917.