Were the US bombings of Hiroshima and Nagasaki justified?

Nuclear weapons did not end the War, the USSR did

Question: Were the US bombings of Hiroshima and Nagasaki justified?
Position‹2 of 2: No, the bombings of Hiroshima and Nagasaki were not justified
Argument1 of 2›: Nuclear weapons did not end the War, the USSR did

Soviet intervention in the conflict was much more important in ending the War in the Pacific.

The argument

At the end of the war Japanese military and civilian leaders considered two strategies to force an acceptable end of the conflict. First, they could ask the Soviet Union, at that point not engaged in the War in the Pacific, to mediate terms of surrender between Japan and the Allies. Second, Japan could fight a final defence of the Home Islands so costly it would force the United States into negotiation. Both of those plans changed drastically when on 9 August the USSR entered the war on the side of the Allies. After quickly sweeping up Japanese units in Manchuria, the Soviets were poised to attack Japan from the North. The USSR entering the war and crushing Japanese forces in Manchuria so swiftly meant both options favoured by Japanese leaders were no longer viable. Japan could not ask the USSR to mediate a surrender if they were a party in the conflict. The military could not fight a two front invasion, particularly given how vulnerable the northern Home Islands were given the concentration on defence against American attack to the South. Soviet intervention in the conflict rally brought an end to the war. Bombing Hiroshima and Nagasaki was not required to end the conflict and so not morally justified.

Premises

[P1]By late in the war Japan's leaders weighed two strategies: asking the still-neutral USSR to mediate surrender, or fighting a costly final defence to force negotiation. [P2] Both plans collapsed when the USSR entered the war on 9 August, swept Japanese forces in Manchuria, and prepared to attack from the north. [P3] It was the Soviet entry, not the atomic bombs, that removed Japan's remaining options and forced surrender. [C] Therefore, the bombings of Hiroshima and Nagasaki were not justified, since the USSR rather than nuclear weapons ended the war.

Counter-arguments

The claim that Soviet entry, not the atomic bombs, ended the war is one influential historical interpretation — associated with revisionist accounts such as Tsuyoshi Hasegawa's — but it is disputed among historians rather than established. The timeline is genuinely ambiguous: Hiroshima was struck on 6 August, the Soviets entered Manchuria on 9 August, Nagasaki was bombed the same day, and Japan surrendered on 15 August, so the two shocks are tightly interleaved and disentangling their relative weight is contested. Notably, Emperor Hirohito's surrender broadcast cited 'a new and most cruel bomb' as a reason for capitulation, evidence that the bombings figured in the decision at the highest level, and traditional accounts hold they were decisive or jointly decisive with the Soviet declaration. Even if one grants that Soviet intervention was the more important cause, the moral conclusion does not follow automatically: whether the bombings were justified depends on what decision-makers reasonably believed and foresaw at the time — including the anticipated cost of invading the Home Islands — and on which ethical framework is applied, not solely on a retrospective judgement of which event actually forced surrender. The argument packs a contested empirical claim and a separate moral inference into one, and the Manchuria point settles neither on its own.

Rejecting the premises

[Rejecting P2] That the USSR's entry removed Japan's options is one influential thesis but is historically disputed; the Emperor's surrender broadcast cited 'a new and most cruel bomb', and the compressed 6–9 August timeline leaves the decisive factor contested. [Rejecting P3] Even if Soviet entry was decisive, moral justification turns on what decision-makers reasonably believed and foresaw at the time and on the ethical framework applied, not solely on which event in hindsight forced surrender.