Soviet Union
officially the Union of Soviet Socialist Republics (USSR), the political entity in existence from the 1917 Bolshevik Revolution to the early 1990s that encompassed modern-day Russia and fifteen neighboring countries. With a communist economy and totalitarian system of government, the Soviet Union grew to be the other major superpower in the post–World War II era. As such, it was the principal antagonist of the United States during the Cold War.