The Union of Soviet Sovereign Republics (USSR; Soviet Union) , previously known as the Union of Soviet Socialist Republics, is the one of the three dominant superpowers in the world. It is the world's largest country and third largest economy. After the Union Crisis of 1991, several of the republics seceded from the USSR and established their independence. After the turbulent reform period of the 1990s, the USSR has regained their temporarily weakened strength and continues to be recognized as a major superpower.