>>These bombings quickly brought the war to a close.

>According to other narratives by historians, the main cause of the Japanese surrender was the Russians entering the Pacific war.

Both - USSR entering the war and the nuclear bombs caused the Japanese surrender. It would have happened soon even without the bombs anyway. The main role the bombs played is to avoid USSR actually invading Japan territory. Ultimately that saved Japan from the Korea and Germany fate.

https://en.wikipedia.org/wiki/Soviet%E2%80%93Japanese_War

"The invasion of the second largest Japanese island of Hokkaido, originally planned by the Soviets to be part of the territory taken,[18] was held off due to apprehension of the US' new position as an atomic power."

>"The invasion of the second largest Japanese island of Hokkaido, originally planned by the Soviets to be part of the territory taken,[18] was held off due to apprehension of the US' new position as an atomic power."

I checked the citations for that part of the article and they do not back up that claim. They are talking about what territory the USSR will get and which surrendering troops will become Soviet POWs. There is no discussion of "well, we better hold off because the 'mericans are just gonna glass 'em all for us".

Furthermore, the Americans had a shovel ready invasion plan with a start date in November. The soviets didn't have a real plan yet. It's not like they called off an invasion because we started lobbing nukes.

Anyone who says that showing the USSR what we were capable of was more than just a side benefit understand the Pacific campaign. If we didn't nuke them we were going to firebomb them. It was basically common knowledge that these people were dedicated enough to follow their cause to the death. What was learned on Iwo Jima and confirmed on Okinawa was that they were going to make us fight for every inch. In lieu of that it's hard to justify not using every available means to kill them dead enough that they surrender without invasion or soften them up prior to invasion. Imagine the scandal has Truman just decided "this whole atom bomb thing is barbaric, we're going to invade them and/or let the soviets burn half a million lives invading them".

Before the bombs were dropped the Japanese had already intimated that they were willing to surrender with one condition: that the emperor would stay emperor. The U.S. wanted an unconditional surrender, but in the end accepted a conditional surrender while calling it unconditional in public. Stalin's entrance in the war sharpened minds on both the Japanese and American side, as neither wanted Stalin involved anymore.

It's hard to prove exactly, but Stalin's entrance into the war is almost certainly the precipitator for it's quick end without an invasion. For the Japanese, partial occupation by Red Army troops was a much worse prospect than occupation by American troops. For the U.S., giving Stalin a say in Japan was utterly unnecessary and very much undesirable at that point (as opposed to much earlier in the war). The A-bombs wouldn't have moved the Japanese military or emperor very much: they weren't more devastating that fire bombing already had been, and there weren't any notable cities left to devastate in Japan.

I may not have stated this well enough, but my original interest was sparked more by the fact that there is a variation of beliefs in the story, than neccesarily what the original motivations truly were in history, as I was wondering about the resulting implications in strategic game theory. MAD only works if all sides have the same standard for destruction in their beliefs and probability measure for the word assured. The US political culture has a general view that nukes end a war, if the political culture in other countries think that it is possible to develop strategies where you can get nuked and still continue with the war, then that is very important thing to be aware of.