The Union of Soviet Socialist Republics (USSR) was a federal socialist state that existed from 1922 to 1991. It was made up of multiple republics, with the largest being Russia. The USSR was founded after the Russian Revolution and aimed to create a classless society based on Marxist principles. The government was characterized by a single-party system led by the Communist Party. The USSR played a significant role in global events, particularly during the Cold War, when it was a major rival to the United States. Its dissolution in 1991 led to the independence of its republics and significant political changes in the region.