The United States fought North Vietnam in the 1960s and 1970s primarily to _________.

During the Vietnam War, a central aim of the United States was to prevent the spread of communism. At the time of the war, North Vietnamese communist forces threatened South Vietnam, and the United States came to the aid of the South Vietnamese government. The Domino Theory of communism held that one nation's conversion to communism was likely to lead to other nations in that region also converting to communism. The aim of the United States was essentially negative (to stop communism) rather than positive (to implement a specific kind of democracy).