The decisive factor in their unconditional surrender was the entry of the Soviet Union into the Pacific war against Japan

Australia: The Next Nuclear Weapons Power? Ramesh Thakur January 18, 2018

The belief in the coercive utility of nuclear weapons is widely internalised, owing in no small measure to Japan’s surrender immediately after Hiroshima and Nagasaki. Yet the evidence is surprisingly clear that the close chronology is a coincidence. In Japanese decision-makers’ minds, the decisive factor in their unconditional surrender was the entry of the Soviet Union into the Pacific war against Japan’s essentially undefended northern approaches, and the fear that the Soviets would be the occupying power unless Japan surrendered to the US first. Hiroshima was bombed on 6 August 1945, Nagasaki on 9 August. Moscow broke its neutrality pact to attack Japan on 9 August and Tokyo announced the surrender on 15 August.