As it was, the Japanese leadership knew that the US had an A-bomb program. Their scientists understood the physics involved and Japan hired neutral Portugal to spy on the Manhattan Project. The Portuguese did a surprisingly good job of it. As Japan's military built tunnels deep in the mountains so they could withstand conventional bombing and battle the expected American invasion to the death, the Emperor looked to the dropping of A bombs as the moment to push for peace. Even after surrender was agreed to though, a faction in the Japanese military attempted a coup in order to keep fighting.
Remarkably, even as the Japanese Bushido code endorsed a glorious death in combat, it also put those who surrendered at the mercy of the victors. And in one of those happy outcomes that are so rare in history, the American victors were not just merciful but were charmed by the Japanese as a people, with General Douglas MacArthur becoming a great peacemaker and reformer of Japanese society.
As WW II combat veteran and later literary critic Paul Fussell put it in the title of an essay and book: "Thank God For the Atom Bomb."
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