There is contentious debate among scholars about why Japan surrendered in World War II. Some believe the Aug. 15, 1945, declaration was the result of the atomic bombs dropped on Hiroshima and Nagasaki.
It's possible that these finally pushed Emperor Hirohito (posthumously called Emperor Showa) to break the deadlock in the Supreme War Council and accept the terms of the Potsdam Declaration for unconditional surrender issued by the Allied leaders on July 26, 1945. In that declaration, there was a promise of "prompt and utter destruction" if the armed forces of Japan didn't surrender. The use of weapons of mass destruction causing the incineration of large swaths of Hiroshima and Nagasaki in quick succession backed up that threat, highlighting the futility of continuing the war. Emperor Hirohito's intervention on the side of those favoring capitulation was crucial to winning over those hardliners who didn't. In this narrative, the dawning of the nuclear age brought peace. It also allowed military leaders to save face, since they could claim that the war was not lost on the battlefield, and agree to surrender to spare the Japanese people from more suffering.
This meant abandoning ketsu-go, the strategy of fighting one last decisive battle intended to inflict so many casualties on a war-weary America that it would relax its demands for unconditional surrender and negotiate a peace. This would, at a minimum, safeguard the Emperor, and potentially preserve the armed forces and shield them from prosecution for war crimes. This strategy was affirmed in June 1945 as the gruesome and bloody Battle of Okinawa was winding down. Reinforcements had been transferred from Manchuria to bolster the defense of Kyushu where the U.S. was expected to attack next.