The United States was a power in the Western Bloc during the Cold War opposed to the Soviet Union in the Eastern Bloc.
The Cold War was a state of geopolitical tension after World War II between powers in the Eastern Bloc ( the Soviet Union and its satellite states ) and powers in the Western Bloc ( the United States , its NATO allies and others ) . The Cold War split the temporary wartime alliance against Nazi Germany , leaving the Soviet Union and the United States as two superpowers with profound economic and political differences . The USSR consolidated its control over the states of the Eastern Bloc , while the United States began a strategy of global containment to challenge Soviet power , extending military and financial aid to the countries of Western Europe ( for example , supporting the anti-communist side in the Greek Civil War ) and creating the NATO alliance . United States . The end of the Cold War and the dissolution of the Soviet Union in 1991 left the United States as the world 's sole superpower .