The Vietnam War was a proxy war between North Vietnam, supported by its communist allies, against South Vietnam and the United States from 1956 to 1975. It began as an extension of the First Indochina War between North and South Vietnam and grew into a wider conflict that also involved Laos and Cambodia. Over 3 million people were killed in the long and costly war, including 58,000 Americans, before ending with the withdrawal of U.S. forces in 1973 and the unification of Vietnam under communist control.