Explain the Domino Theory as a reason for U. S. involvement in Vietnam.

After Vietnam was split up into two countries (north and south Vietnam) North Vietnam fell to communism and since the domino theory means if one nation falls to communism the rest will fall to communism it meant that South Vietnam will also fall to communism and the US has been trying to stop communism for a long time and we also have a relationship with South Vietnam and the leader of that country we could not let it fall because that would mean the rise of communism in all of Eastern Europe and eventually lead to communism crossing into our country and that could not happen which led us into war with Vietnam