The Soviet Union, officially the Union of Soviet Socialist Republics (USSR), was a transcontinental country that spanned much of Eurasia from 1922 to 1991. It was a successor state to the Russian Empire that 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. As a one-party state governed by the Communist Party of the Soviet Union, it was a flagship communist state.

The Russian Empire, also known as Imperial Russia or simply Russia, was a vast realm that spanned most of northern Eurasia from its proclamation in November 1721 until its dissolution in March 1917. At its height in the late 19th century, it covered about 22,800,000 square kilometres (8,800,000 sq mi), roughly one-sixth of the world's landmass, making it the third-largest empire in history, surpassed only by the British and Mongol empires; it also held colonies in North America between 1799 and 1867. The empire's 1897 census, the only one it conducted, found a population of 125.6 million with considerable ethnic, linguistic, religious, and socioeconomic diversity.