The Post World War II period of the Twentieth Century was dominated by two international themes: The Cold War and the End of European Colonialism. During World War II, the capitalist United States and the communist Soviet Union, which included Russia, were allies. Both had a common goal. The defeat of Nazi Germany. Once the War was over, the two great powers of the US and the Soviet Union saw each other as an adversary. This contest between the two continued until the fall of the Berlin Wall in 1989. Though adversaries, the two did not conduct a "hot war" of military fighting. Instead they pursued a Cold War, "an undeclared conflict characterized by spying, hostile propaganda, sabotage, and economic embargo" (Strain, p. 6). This competition dominated international relations in the post-World War II period.
Note: The Soviet Union is short for the Union of Soviet Socialist Republics (U.S.S,R.) that existed from 1922 to 1991. It was a federation of Communist states, led by Russia, under one sovereign government.