NATO stands for the North Atlantic Treaty Organization, which was basically a treaty signed between the United States and 11 other Western nations. These people did not believe in communism and was put together in 1949. This treaty is still round today. When the other communists heard about this pact, they decided to form another alliance. The Soviet Union and the Eastern nations put together a rival alliance, called the Warsaw Pact in 1955. During the late 1990s, some eastern nations joined the NATO alliance and caused tension between them and the Soviet's after the Cold War.