Many (most?) historians believe that the Soviet entry into the war induced the Japanese surrender. Some historians believe that American decision makers expected Japan to surrender soon and wanted to use atomic bombs before the end of the war, to demonstrate their power to the Soviets. Gaddis Smith:
It has been demonstrated that the decision to bomb Japan was centrally connected to Truman's confrontational approach to the Soviet Union.
A very small number of historians believe that the atomic bomb on net cost American lives. Martin Sherwin:
Many more American soldiers... might have had the opportunity to grow old if Truman had accepted Grew's advice. [that all that would be needed to induce Japanese surrender starting in May was explaining that US occupying forces would follow the rules of war, not exploit the Japanese, etc, and that delaying to use the atomic bomb was wasteful]
Some historians believe that American decision makers expected Japan to surrender soon and wanted to use atomic bombs before the end of the war, to demonstrate their power to the Soviets.
I favor this hypothesis, it seems to me the demonstration of the power of atomic bombs was as much for Stalin's benefit as it was for the Japanese leadership's. One can make a reasonable case that Hiroshima and Nagasaki were the real reason why the battle-hardened Soviet army stopped in Germany and didn't just roll over the rest of Western Europe.
Another month has passed and here is a new rationality quotes thread. The usual rules are: