From 1945 - 1990, the United States was involved in a war with The Soviet Union. Historians do not agree on when the war actually started but they do agree that it was sometime around the end of WWII in 1945. During the Cold War intense rivalry existed between groups of Communist and non-Communist nations. The Soviet Union was the leader of the Communist group and the United States was the leader of the non-Communist group. Mutual distrust, suspicion, and misunderstandings practically describe the Cold War.
Toward the end of World War Two, Germany continued to fall, so the United States, Great Britain, and the Soviet Union met in the Soviet city of Yalta. This meeting was called the Yalta Conference. At this conference, the three nations planned to discuss their objectives on what to do with the German territories. Some of their goals included promoting world peace, providing emergency relief, and helping set up a temporary government based on the will of the people. Both Stalin (the leader of the Soviet Union at that time) and Roosevelt (leader of the United States) had different views on achieving those goals. .
While at the Yalta Conference, the three nations; United States, Great Britain, and the Soviet Union, developed the Declaration on Liberated Europe. This declaration meant that the three nations agreed to hold democratic elections in countries freed from the control of Germany. The Soviet Union did not keep its word and broke this agreement. Stalin had driven German troops out of parts of Europe and had established a communist government in Poland. This caused the United States to feel betrayed by the Soviet Union and also led the United States to consider the Soviet Union untrustworthy.
At this point in time, neither the United States nor the Soviet Union trusted each other. They accused each other of trying to rule the world. The United States accused the Soviet Union of trying to spread communism throughout the world and the Soviet Union accused the United States of practicing imperialism, which means that they were trying to extend their power by gaining land, and of trying to stop revolutionary activity in other countries.