Better than most articles on the topic.
Japan’s Longest Day —one of the best books on the desperate attempts of the Japanese to end the war in the closing days.
They kept trying to recruit the Soviets as an intermediary in arranging a conditional surrender; they knew that the Yalta Conference required the Soviets to participate in the downfall of Japan within 6 months of Hitler’s fall, so they were curious about what kind of role Stalin might play.
Greedy to get his hands on Japan lands (he captured 2 or their islands, which remain in their hands to this day), Stalin of course SIMPLY DIDN’T CALL BACK. Repeatedly.
So the Japanese could see the writing on the wall —Stalin would let them twist in the wind and if the war went on much longer Soviet troops would likely be on the beaches, somehow, somewhere.
The Americans understood the 6 month clock was running, that the Soviets would get involved, and they wanted to keep them out and avoid the type of cutting-up on Europe that was already going on.
The atomic bombs gave the Americans a way to beat the clock and keep the Soviets out.
The Japanese understood if the Soviets were deeply involved their Emperor would share the fate of the Tsar 30 years earlier.
I’m surprised Stalin didn’t try to keep them on the line longer to try and get his assets into place. Although they were probably stretched pretty thin with everything in Europe and the purges within the Soviet military.
And according to a story related by talk show host several years ago, the U.S. flew to Finland several aircraft similar to the Enola Gay and simply parked them at an airport - in full view of the Soviet Union, implying they had more in their hip pocket. A quiet threat and a major bluff.
The Yalta agreement required the Soviet Union to declare war and attack the Japanese with 90 days of the German surrender. Marshal Vasilevsky’s attack on the Japanese in Manchuria was launched on August 9th.