War crimes in Vietnam.
Just a couple.
The US dumped Agent Orange indiscriminately, certainly on jungles, also on people and rice paddies, destroying them and the food supply. In this case Agent Orange was a chemical WMD.
The commander of the Marine Corps told troops that every dead Vietnamese was a badguy, inflating the body counts. That meant the men, women, children were counted as Viet Cong no matter how guilty or innocent.
I won't go so far as to say the US troops were war criminals. I will say the US committed many, many war crimes in a land far, far away which posed no threat to the US.
Arf