Answer: communism
Explanation: The United States main concern during the Cold War was communism. The Cold War was not a traditional war. It was "cold" because the U.S. and the Soviet Union did not fight each other directly. The Cold War began after World War II ended in 1945. The Soviet Union was a communist country. Communism is an economic system where most property belongs to the government. The United States had a capitalist economy, where property usually belongs to individuals. The United States and the Soviet Union competed for world power. Leaders of both countries worried that the other would use the atomic bomb to turn the Cold War into a real war. This never happened. The Cold War ended in 1991 when the Soviet Union divided into many smaller countries. The United States' main concern during the Cold War was communism.