Really Japan’s surrender can’t be pinned on one issue alone. It was the combination of different events that finally pushed the Emperor to issue the go-seidan overruling the ministers and accepting the Potsdam declaration (well, almost anyway but I’ll get to that).
The Emperor had already made it clear to the Diet previously that he wanted his ministers to work toward ending the war. At that time for Japan, they were limited in what channels to use to negotiate a peace. Russia was the best conduit for that since they were not at war with them at the time and could serve as a mediator in negotiating a peace rather than just accepting “unconditional surrender”.
The ministry would put out a feeler to Molotov on July 13th, to try to open the door to mediation. The request would be ignored by Russia, much to the consternation of Diet until the night of the 8th of August when the answer would be a declaration of war instead of a channel of negotiation.
The sticking point for Japan was the “unconditional” aspect of the demands placed by the Allies. There were several things Japan wanted to negotiate for a peace, but a non-starter was leaving the fate of the Imperial house to the Allies. There was fear among the ministers and the Emperor that accepting “unconditional” surrender would leave the the Emperor vulnerable to war crime charges. Had the conditions of the Potsdam Declaration included a provision that could have left the Imperial house intact, there is every possibility that Japan may have surrendered before the first atomic bomb was even dropped (we will never know for sure of course).
After the destruction of Hiroshima, the conversation in the Diet did change. The Emperor is said to have made the observation that with this kind of weapon in use, it was even more impossible to continue the war. He then suggested that the ministers should not miss any opportunity to end the war at the earliest possible moment provided that it was under a “favorable term”. Though the atomic bomb had not convinced the Japanese to end the war, it had instilled in them, and the Emperor, a sense of urgency to get an acceptable surrender negotiated (”unconditional” still being a sticking point).
On the evening of August the 9th, over 12 hours after the second bomb struck Nagasaki, the Diet met again. An interesting anomoly of this meeting is that the atomic bombing of Nagasaki was not really discussed though it is certain that they knew of this second attack. The only reference even close was made by the Chief of the Army General Staff Yoshijiro Umezu who was totally against surrender and stated that there was no reason to surrender as a result of air raids (which would include atomic raids).
What was discussed extensively was the Soviet declaration of war. The talks were not so much on the operational level as they were the political one. That avenue that they had hoped to open to negotiate a peace had suddenly been closed on them. With the exception of the hard liners who would never accept peace, the rest of the Diet had come to the conclusion that the Potsdam Declaration would have to be accepted.
This still didn’t keep them from trying to negotiate terms. Even on that evening of the 9th, the initial proposal called for four conditions for peace.
1. The terms will not include andy demands on the Imperial House.
2. Japanese military units abroad will be allowed to voluntarily withdraw and demobilize.
3. War criminals and their trials will be handled by the Japanese govenment.
4. There will be no occupation of the Japanese home territory.
By the end of the meeting cooler heads had put forward the fact that if they expected to get any concessions to “unconditional” at all, they should be very limited in what they asked for. The final text approved by the Diet read as follows:
“The Japanese Government is ready to accept the terms ennumerated in the tripartite joint declaration which was issued on the 26th of last month, with the understanding that the said declaration does not comprise any demand which prejudices the prerogatives of His Majesty as a sovereign ruler.”
They opted to only ask for that first and most important condition, protecting the living decendent of Amaratsu on earth.
So the go-seidan (sacred decision) issued by the Emperor was driven just as much by the declaration of war by Russia as it was the atomic bomb, and the fact that they were, at this point, completely cornered and materially exhausted. All of these factors came together to convince the ministers and the Emperor to go ahead and accept the terms for surrender while asking for just the one caveat.
Would the war had ended with just the atomic bombs? The evidence makes it seem unlikely, but it really is a bit speculative. If that had been the only factor, there would not have been that other pressure with the Soviet declaration of war and maybe the bombing of Nagasaki would have sunk in more completely compelling the same result. There is no way to know. We can say certainly that the atomic bomb did create a sense of urgency in Japan to end the war.
Do we give credit to the Soviet invasion? Honestly, the invasion itself really didn’t have any bearing on the decision. The Army staff in Tokyo still stated that they believed they could defend Manchuria from the Soviets despite the initial setbacks. It was delusional for certain, but they believed it emphatically. It was the loss of that perceived channel of negoatiation that had the real impact on the Japanese decision. So it wasn’t the act of war, just the declaration of it that really forced Japan’s hand.
Those two items along with the desparate situation that Japan was already in led to their final decision to “endure the unendurable” and surrender.
Interesting take. Thanks.