After WWII the United States and the Soviet Union were in an open but restricted conflict called the Cold War.
The Soviet Union wanted to spread communism world wide, soon after the end of the war it had already installed left-wing governments in eastern Europe. The U.S. feared the spread of the communist ideology, under the Marshall Plan , it provided aid to Europe in order to recover and resist the Soviet Union. It is called Cold War because these superpowers didn't fight directly between them, they used politics, economics, and propaganda tactics to fight, the actual battles were fought in periphery countries. An example is the Vietnam war, which lasted until 1975. The Cold War lasted until the collapse of the Soviet Union in 1991, but it was already very weak in the late 80's.
