The Russian Empire (Pre-reform Russian: Pоссiйская Имперiя, Modern Russian: Российская империя, translit: Rossiyskaya Imperiya) was a state that existed from 1721 until the Russian Revolution of 1917. It was the successor to the Tsardom of Russia, and the predecessor of the Soviet Union. It was one of the largest empires the world had seen. At one point in 1866, it stretched from eastern Europe, across northern Asia, and into North America. At the beginning of the 19th century, Russia was the largest country in the world, extending from the Arctic Ocean to the north to the Black Sea on the south, from the Baltic Sea on the west to the Pacific Ocean on the east. Across this vast realm were scattered the Tsar's 150 million subjects, from poor, illiterate peasants to the noble families of great wealth. Its government, until 1906, was controlled by the Tsar, who was supreme autocrat.