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?
I thought Japan's war in China was going fine. It was the war in the Pacific that was going badly.
Japan was in no danger of losing in China. They were hip deep, of course, because China is virtually unconquer-able, but they weren't actually losing.
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.
The Soviet invasion of Manchuria destroyed their logistics chain, caused a majority of their force in the North to rout, and basically made field operations in China impossible. They'd have lasted 3 months tops with 1.5 million Soviet Guards pressing from the north.