The Union of Soviet Socialist Republics[r] (USSR),[s] commonly known as the Soviet Union,[t] 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.[u] 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;[v] in