What was the us policy that required the us to fight in the vietnam war

The U.S government viewed its involvement in the war as a way to prevent a communist of South Vietnam.This was part of the domino theory of a wider containment policy, with the stated aim of stopping the spread of communism world wide :source: https://en.m.wikipedia.org/wiki/Vietnam_War

Communicating with the dead was common, it wasn’t seen as bizarre or weird,” explains murch. “it’s hard to imagine that now, we look at that and think, ‘why are you opening the gates of hell? ’