Is that what you think you were doing in Vietnam...defending the United States?
That is an objectively false notion, and there is 50 years of post war history to confirm it.
Once again, I'll write slowly for you, so you can catch up: Vietnam was the first ever employment of the Soviets' "National Liberation War" strategy, a form of "assisted suicide" where the Sovs and their best friends armed, supplied and trained the North so they could conquer the South. You may not be aware of it, but we were in a global struggle against the Soviets, the Warsaw Pact, and China back then and they chose Vietnam as the next push for expanded power. We who volunteered and fought in Vietnam were protecting our country and the South Vietnamese and in turn all of our allies in the area.
I suspect that we did that without your help.
The "histories" you cite were written by the same Leftists who campaigned for the NVA in the guise of "antiwar" activists.
Your "50 years of history" don't confirm anything. You weren't there.