The Cold War began at the end of World War II for several reasons. The United States and the Soviet Union had economic and political systems that were opposites of each other. The Soviet Union wanted to spread their system around the world. They began to break agreements that we had made with them before the end of the war. We felt we needed to prevent the spread of Communism. We didn’t want to be surrounded by communist countries.
The Soviet Union refused to leave northern Iraq at the end of the war. We had to threaten military action to get them to leave. The Soviet Union tried to spread Communism to Greece and Turkey. We offered these countries economic aid, and they stayed noncommunist. The King of Romania said he was pressured to have a communist government even though the Soviet Union agreed to the Declaration of a Liberated Europe. This agreement would allow countries to choose the kind of government they wanted to have. The Soviet Union violated this agreement.
In each instance, the United States challenged the Soviet Union. This created a period of confrontation and competition between the United States and the Soviet Union. This was called the Cold War.