ˌSoviet ˈUnion, the BrE AmE
between 1917 and 1991, a country in Europe and Asia, whose full name was the Union of Soviet Socialist Republics (the USSR). The Soviet Union was the largest country in the world and was made up of 15 ↑ republic s (=separate nations) , the most important of which was Russia. It was formed after the ↑ Russian Revolution in 1917 as a Communist state, led by ↑ Lenin . For a long time it was one of the most powerful countries in the world, with a large army and many modern weapons, and it was regarded as the enemy of the US and western Europe during the ↑ cold war . Its political system was controlled by the Communist Party. Ordinary people had little power and were not allowed to leave the Soviet Union, although a small number of people defected (↑ defect ) to the west (=escaped to live in other countries) . Mikhail ↑ Gorbachev , who was leader of the Soviet Union from 1985 to 1991, introduced many political and economic changes and, partly as a result of this, the Soviet Union began to break up as many of the republics got rid of their Communist governments and made themselves independent. ⇨ ↑ glasnost , ↑ Gorbachev, Mikhail , ↑ perestroika , ↑ Stalin