Think it was January 1943 that FDR said the Allies expected “Unconditional Surrender” from the Axis. Later, he said it wasn’t a considered statement – that Grant’s famous phrase popped into his head and he liked the sound of it. Was that true, far as anyone knows? Does everyone now agree that it was a bad idea to say it?
People like to say that Japan was “trying to surrender” before 6 August; what they presumably mean is that Japan was trying to negotiate a conditional surrender, but the Allies didn’t feel like going back on Roosevelt’s promise. “Negotiate” means saying “If you do A, we will do B.” The corollary is, “If you don’t do A, we won’t do B.” Japan couldn’t “negotiate” without at least pretending to be willing to fight forever. After Okinawa, the pretense would have had some weight.
Some people in Japan wanted to negotiate a surrender, but not any of the people with the power to make it actually happen. The people who had the power wanted unconditional war.
A demand for unconditional surrender might have been unwise, but in the end, it worked anyway.
A negotiated surrender is just a continuation of the war.
Negotiated terms for the end of conflict is different. Like in the Civil war the rebels were allowed to go home and keep their firearms because those were probably the most valuable things these defeated solders had, they would be needing them for hunting and things.
The commitment to unconditional surrender came from the Casablanca Conference; it didn’t just pop into FDR’s head. FDR borrowed the phrase from Grant, but it was the joint policy of the US and the UK at the Conference. Behind the scenes, Churchill wasn’t a strong supporter of the concept, but it was considered an important statement for Stalin to hear from the western leaders.
The point of “unconditional” is complete regime change. The current sitting government of the losing side will be comprehensively dismantled by the winning side. And something to the winner(s)’ liking installed in its place.
Which is what it takes to prevent the same losing leadership’s people from restarting the same war as soon as they’re able.
So it’s not real popular with anyone in authority on the losing side.
Also, the “unconditional surrender” strategy was formulated with Germany in mind. The allies did NOT want something like the “stab in the back” legend to take root again in Germany like at the end of WW1 (which led to revanchist tendencies and was considered to be an important factor that led to WW2). This time they wanted Germany to know and acknowledge that they were utterly, completely defeated, with no wiggle room for revanchist explanations “ex post facto”.
Which is also why the Allies insisted that the Instrument of Surrender be signed by the highest ranking military that were available. Doënitz, claiming to be the new leader of the German government, was not a signatory.
The Preamble states:
The German Government and German High Command, recognizing and acknowledging the complete defeat of the German armed forces on land, at sea and in the air, hereby announce Germany’s unconditional surrender.
I don’t think it even it has reached that point, they had sent out “peace feelers” to third parties, basically offering to begin negotiations about beginning negotiations. For the most part the US only found out about them because they had cracked the Japanese code, they never received the actual message from Japan directly.
Until virtually the very end, Japanese leaders thought that the Allies could be worn down enough by high casualties that they’d agree to peace terms permitting Japan to hold on to at least some of its conquests, as well as maintaining their current government. Indicating willingness to negotiate such terms would probably have emboldened the Japanese war hawks further.
The allies would’ve probably eased the Japanese surrender if they had agreed to allow the emporer to maintain some sort of ceremonial and nominal role as the head of the Japanese government which they ended up doing anyway to ease the transition to the new government and reduce resistance. That was an important sticking point to them and didn’t seem to cost the allies much.
On the other hand, the acceptance of complete defeat seemed to work out well for Japan in the post war recovery, where they had a remarkable transformation, very much embraced American ideas of how to run a society, and ended up being very prosperous in the decades after the war, and to some degree it was the complete defeat to the allies that lead to that, so perhaps it worked out for the best in any case.
It was much more substantial than that. The Japanese government was instructing their ambassador to the USSR to send out feelers to the Soviet government:
On 30 June, [Foreign Minister] Tōgō told Naotake Satō, Japan’s ambassador in Moscow, to try to establish “firm and lasting relations of friendship.” Satō was to discuss the status of Manchuria and “any matter the Russians would like to bring up.”
On 12 July, Tōgō directed Satō to tell the Soviets that:
His Majesty the Emperor, mindful of the fact that the present war daily brings greater evil and sacrifice upon the peoples of all the belligerent powers, desires from his heart that it may be quickly terminated.”
The Emperor proposed sending Prince Konoe as a special envoy, although he would be unable to reach Moscow before the Potsdam Conference.
On 21 July, speaking in the name of the cabinet, Tōgō repeated:
With regard to unconditional surrender we are unable to consent to it under any circumstances whatever. … It is in order to avoid such a state of affairs that we are seeking a peace, … through the good offices of Russia
Those were not unauthorized feelers.
(Unfortunately for the Japanese, they didn’t realise that the Soviets were busy planning the invasion of Manchuko and Hokkaido, so were not dealing in good faith.)
(Plus the US had broken Code Purple and so were gaining the Japanese diplomatic cables almost as soon as they were sent out.)
(Quotes from Wikipedia article on the Surrender of Japan.)
I’m not sure you could accurately characterize said feelers as “substantial”. In the end, they amounted to very little, because the Imperial Supreme War Council was divided on the question of what their peace stance should be, and thus Sato (the Japanese ambassador to the USSR) had little to offer the Soviets beyond platitudes. In any case, the War Council’s consensus stance on peace at the time was utterly incompatible with that of the Allies - they wanted no occupation, no Allied trials of Japanese war criminals, no changes to the Japanese government, and no relinquishment of overseas territories seized by Japan prior to 1937.
As late as August 2nd, a full week after the Potsdam declaration had been issued, the Japanese foreign minister told the ambassador that:
it is difficult to decide on concrete peace conditions here at home all at once.
…implying that the War Cabinet remained split on what they should offer in peace negotiations. Which is understandable - a week later, after the shocks of Hiroshima, the Soviet entry into the war, and Nagasaki, the cabinet was still split 3-3 on whether to accept the Potsdam declaration or continue fighting.