For what reasons did we fight the Vietnam war?

We fought over the way the government in Vietnam was being run. They had communism which means if someone needed something in Vietnam like food or money, it was given to them. But we wanted them to have democracy, which means the exact opposite, if we wanted something, we would have to earn it. If we wanted $10, we would have to work to earn the money. So we fought with Vietnam just because we wanted them to have democracy.

P.S. We're mean!