The Pacific Theatre

In The Winning Weapon? Rethinking Nuclear Weapons in Light of Hiroshima, Ward Wilson argues that, setting aside the issue of whether the atomic bombings of Hiroshima and Nagasaki were necessary to bring about an end to the war (the usual basis for justifying them morally), examining Japanese government cabinet papers suggests that the bombings were not even sufficient, not being decisive in convincing the Japanese to surrender - the Soviet declaration of war was:

In the summer of 1945, Japan’s leaders had two strategies for negotiating an end to World War II: to convince the Soviets (neutral at the time) to mediate, or to fight one last decisive battle that would inflict so many casualties that the United States would agree to more lenient terms. Both plans could still have succeeded after the bombing of Hiroshima; neither plan was possible once the Soviets invaded. From the Japanese perspective, the Soviet invasion of Manchuria and other Japanese-held territory was the event that dramatically changed the strategic landscape and left Japan with no option but to surrender unconditionally. The Hiroshima bombing was simply an extension of an already fierce bombing campaign.

A PDF file of the article is available at the site linked above; Freeman Dyson summarises Mr Wilson's argument in his answer to The Edge Annual Question for 2008. (H/t to a sorry little doggy.)