The United States was in a state of geopolitical tension with the Soviet Union after World War II.
The aftermath of World War II was the beginning of an era defined by the decline of the old great powers and the rise of two superpowers : the Soviet Union ( USSR ) and the United States of America ( USA ) , creating a bipolar world . 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 . 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 .