"But I was always under the impression the historic line is that the nukes weren't the key catalyst for Japan surrendering."
I agree, as the Japanese leadership had long realised that their position was untenable.The standard story says that the justification for dropping the bombs was the saving of millions of lives that would have otherwise been lost if Japan were to be invaded.
"Russia invading Manchuria made the Japanese fear they would be forced to give up their soverignty to Russia."
I think that they were more worried about being invaded by Russians as they no doubt knew that they had lost Manchuria.
"The American firebombing was far worse anyway." Too true, though that isn't a justification if they were trying to surrender anyway.
"The nukes were a nice excuse for everyone and America had to do something with their incredible expenditure."
The article does mention that. There are quotes by some key players that stated that the bomb needed to be used in war, not just demonstrated, to justify the huge amount spent on its development. They expected to be made scapegoats if it hadn't worked and would face consequences.
