From 1957 to 1965, the war was mainly a struggle between the South Vietnamese army and Communist-trained North Vietnamese rebels known as the Viet Cong. During this time, the U.S. provided military advisors and China and the Soviet Union supported the Vietnamese Communists with war materials but not troops. The first U.S. combat troops entered Vietnam in March 1965 and most of the fighting was between North Vietnam and the United States. By 1969, the Vietnam War seemed endless, and the United States slowly began to withdraw troops.