This has been discussed here quite a few times, I think most recently in this thread.
In hindsight, the bomb was probably the lesser of other evils. However, it doesn’t completely disguise some other unpleasant factors about the mindset of the US at the time.
The ‘invasion’ of Japan’s main islands would not have been much of an invasion. Almost all the remaining healthy Japanese men above the age of 14 or so were already in the army. The ones not already actually fighting were either old, wounded, crippled, women, or children.
Japan’s military was in shambles. Its airforce was no longer a real threat. As far back as 1942 Japan’s airforce was unable to train enough cadets to replace those lost (at the Battle of Midway Japan lost as many aircrewmen in a single day as their pre-war training program had produced in a year).
Japan had no more resources with which to make weapons, bullets, etc. My grandmother-in-law recalls the government confiscating pots and pans, apparently so the metal could be melted down.
A grandfather-in-law was one of only three people to survive from his company following a battle in the Philippines. He lived in constant shame at being one of the survivors. Up until his death a few years ago he refused to look at the TV if the Emperor or any member of the royal family was on it. The rest of the family looked upon his as a bit kooky, but everyone says that’s how everyone was back then.
I have no doubt believing that Japan would have indeed fought to the very end. Japan’s mindset is such that they find it much easier to take their own life than Westerners. Even today - although it is never spoken out loud - there is still an unspoken agreement among Japanese that someone that committed suicide to atone for a hideous deed has managed to recover a bit of respect and dignity.
So how much resistance would a bunch of women, children, and old men, armed with nothing more than bamboo spears and awls, actually put up? The idea that the US would have faced ‘massive causalties’ in an invasion is just flat-out silly - the US military would have steamrolled the island; I suspect their guns would give a bit of a reach advantage compared to that guy holding the shovel.
Might have taken a while, no doubt, And there would have been some casualties - but this wasn’t going to be a Normandy invasion. Overall, any actual invasion would have been a massive mop-up operation, and both of my grandfather-in-laws not only say this, they say everyone at the time in Japan knew it as well. They fully expected it, and were preparing for what they assumed was inevitable death defending Japan.
Did the US military at the time know this? I suspect they only suspected it; I’m not convinced they were that aware of what was happening on the ground in Japan at the time. And even if they did - I’m not sure it would have mattered. Germany was Europe - it was the former homeland for many Americans. What Japanese Americans went through in WWII was never an issue for German Americans, for example. A lot of people forget that many people (including Charles Lindburgh) were pro-Germany early on. Asia, however, was unknown to most, and the unknown tends to bring out the worst in people. Check out the political cartoons by Dr. Seuss, for cryin’ out loud, at the height of the war. I’ve seen anti-German propaganda from the era as well, but honestly none of it makes me cringe like the anti-Japanese propaganda does (although how much that is because I’ve lived in Japan for so long, I don’t know…).
There were just three days between Hiroshima and Nagasaki. I’ve always thought that three days simply wasn’t enough time for Japan to do anything. Heck, after three days even people in Hiroshima weren’t fully aware of what had happened.
I believe 100% (but have no proof) that the second bomb was 90% because the military wanted to test out another new type of bomb.
I honestly believe that Japan as a country would probably not exist today if the allies had actually invaded. A Japanese politician had to resign not too long ago for admitting what everyone actually thinks - the Japan of today is far, far better off than it would have been if it had been invaded. The downside for me is that Japan is able to use the ‘only country to have nuclear weapons used on it’ card, and it plays the victim a bit too easily. But that’s neither here nor there.