The Union of Soviet Socialist Republics[t] (USSR),[u] commonly known as the Soviet Union,[v] was a transcontinental country that spanned much of Eurasia from 1922 until it dissolved in 1991. During its existence, it was the largest country by area, extending across eleven time zones and sharing borders with twelve countries, and the third-most populous country.[w] An overall successor to the Russian Empire, it was nominally organized as a federal union of national republics, the largest and most