The United States entered the war to stop the spread of Communism in Southeast Asia. American leaders feared that Communist forces would gain control of Vietnam. After that, nation after nation might fall to Communism. Communism is a political and economic system that the United States strongly opposed. Vietnam had been split in half in 1954, after fighting a war to gain independence from France. When French forces withdrew, Vietnamese Communists gained control of North Vietnam. Ho Chi Minh was the leader of the North Vietnamese Communists. South Vietnam had a non-Communist government. This government was weak. But the United States supported it in order to keep the Communists from taking control of all of Vietnam.