the war (c. 1957-75) between North Vietnam and South Vietnam: the U.S. participated on the side of South Vietnam, with its greatest military involvement in the period c. 1965-69
See Vietnam War in American Heritage Dictionary 4
noun
A protracted military conflict (1954-1975) between the Communist forces of North Vietnam supported by China and the Soviet Union and the non-Communist forces of South Vietnam supported by the United States.