Laos and Cambodia weren't participants in the war but that doesn't really feel like it matters all that much. Whenever I talk about the bombings of Cambodia and Laos with Americans (who - liberals and conservatives alike feel they must always defend) I sometimes here "well we bombed cities in Germany and Japan in WW2 and no one talks about those being war crimes". But were they? I really don't know much about those bombings. My gut says yes they were also war crimes but we just accept them because they were combatant countries?
From what I remember there were several million Soviet soldiers ripping through Manchuria when the nukes were dropped, and American command was worried that if they didn't stop the Soviets then the Soviets would invade and occupy at least China, and maybe Japan too.