In February of 1945, the Allies agreed to hold elections in every country they had freed. From the start, the Soviet Union ignored the agreement. Instead, it set up communist government in one Eastern European country after another.
President Truman was outraged. He and later American presidents set out to keep to Soviet Union from taking over any more land. The struggle that followed between the United States and the Soviet Union is called a cold war. A cold war is fought with words and money, not with guns or bombs. At the same time, each side prepares for a war it hopes will never come.
By 1949, the Soviets had their own atom bomb. Soon the two sides were competing in a deadly arms race. Each was determined to produce more weapons, and more destructive weapons, than the other side. The competition between the two countries took other forms too as each tried to win countries to its point of view.