That is a total "history is written by the victors" example though, and thank you for mentioning that. It's also no longer really considered plausible. Japanese soldiers were certainly happier to carry out suicide attacks and the like than American ones (though had the US homeland been under threat, I wonder if much daylight would have fit between them), but there's little real, genuine, compelling historical evidence to suggest that Japan's overwrought and ridiculous defense plans were anything less ridiculous than their other overwrought and ridiculous plans. Other nations had had some fairly exotic plans for what happened if they were invaded, pretty much none of which ever actually happened. Certainly Japanese civilians didn't seem to be any more suicidal than anyone else.
What is perhaps fairer to say is that the US genuinely believed that dropping the bomb would save at least some lives in total. But the most compelling reason I've heard is that the US public would have found it completely unacceptable if it came out, after the war, that the US had this bomb, and didn't use it on Japan. I mean, let's imagine a scenario where the US reaches Japan and starts fighting, the emperor has a heart attack (we can hope!) and his son immediately signs a surrender, and the bomb was never dropped, but maybe 50k US troops are killed closing in on and attacking Japan. That's far fewer people than were killed in Hiroshima and Nagasaki, but no-one would know that. What they'd know was, the US had a superweapon and it didn't use it, and 50k soldiers died perhaps because they didn't use it. Any politicians involved in THAT little decision would be done, generals would likely have to resign, and so on. So the best option for them was to use it and see what happened.
(I'm not actually here to condemn them for it - obviously it was nowhere near as bad as some of the firebomb raids the Allies did in terms of casualties or really even horror. You want to look for real moral wrongs look there. The whole idea of aerial bombardment of civilian populations actually achieving anything was largely debunked by WW2 and also by the Vietnam war, particularly the incursion into Cambodia, where more bombs were dropped by the US than in WW2*)
* = Cite:
Plain of Jars - Wikipedia - look under "Present day" - also an amazing location to think about for D&D.
Strongly agree with you re: war in-game. It's best if it's something that already happened, or is to be averted.