"Very late the next night, however, something happened that did change the plan. The Soviet Union declared war and launched a broad surprise attack on Japanese forces in Manchuria. In that instant, Japan’s strategy was ruined. Stalin would not be extracting concessions from the Americans. And the approaching Red Army brought new concerns: The military position was more dire, and it was hard to imagine occupying communists allowing Japan’s traditional imperial system to continue. Better to surrender to Washington than to Moscow."
American propaganda teaches that Japan's surrender in 1945 happened only because Hiroshima and Nagasaki were incinerated. That mantra is demonstrably false. They surrendered because the Soviets declared war and left them with no way out. The United States is still the only nation that has dropped atomic weapons on human beings and it didn't have to happen. Read here.