And it seems if I put this in my story, it would cause an immense of controversy as it involved so much genocide and horrifying events. I'm not even sure which side I'd be able to put an American soldier on.
There would be no controversy whatsoever. Stop worrying about "controversy". I can't say that to you enough times. No one, absolutely no one, will bat an eyelid. There are literally thousands, if not tens of thousands of works set in those periods. If Nazis don't cause controversy, neither will the Vietnam war. You talk about genocide and horrifying events. You DO know what the Nazis did, right?
I know there's thousands of stories set in that time period but not many I know of about the Cambodian invasion and Pol Pot. Seems that many avoid it. Same with the Nazis. Many have done it, especially in science fiction because it's easy to determine who the good guys and bad guys are. I've rarely heard of any science fiction done with Vietnam and especially involving the Cambodian attack with Pol Pot involved.
What difference does it make if it's science fiction? There are at least five episodes of Quantum Leap set during the Vietnam War. No one bothers with Cambodia because it's not as well known in the American or Western psyche. I'll repeat again. No one is going to give a rat's ass.
I'm closing this thread since its basically a replay of the others* (there does come a point at which we don't need any more threads on the same subject) Two points to take away a) As we may have mentioned once or twice already you can't write you book by committee - make your own decisions, and b) If you want help with setting, plot, research or whatever for the love of the tiny furry Cerberus ask some specific questions * https://www.writingforums.org/threads/need-some-serious-feedback-on-these-characters.164719 https://www.writingforums.org/threads/us-commando-spy-in-the-early-1960s.164712 https://www.writingforums.org/threads/the-age-and-timeframe-of-a-soldier-in-historical-fiction-setting.164697 https://www.writingforums.org/threads/creating-a-fictional-setting-during-the-50s.164576