Eight decades after the destruction of Hiroshima and Nagasaki, the question of whether the atomic bombings were legitimate remains unresolved and structurally central to contemporary strategic thought. The decision taken by President Harry S. Truman is most often framed as the outcome of extreme constraints: Allied exhaustion after years of total war, fierce Japanese resistance, and the prospect of a devastating ground invasion of the home islands. Yet this narrative collides with a deeper moral question: can the deliberate annihilation of cities be justified in the name of saving more lives, or does it represent an absolute rupture with the principles of just war and the protection of civilians? The near-total militarization of Japanese society blurred the line between combatants and non-combatants, anticipating dilemmas that now resurface in urbanized and asymmetric conflicts from Gaza to Ukraine. Hiroshima and Nagasaki also inaugurated a lasting nuclear taboo: an unwritten but powerful prohibition on the use of nuclear weapons, which has helped prevent their re-employment while paradoxically reinforcing their political centrality. Between strategic necessity and radical moral transgression, nuclear weapons have become the ultimate test of our capacity to link power to responsibility. Preventing the return of the unthinkable requires sustaining a demanding synthesis between military prudence, humanitarian law, and an ethic of responsibility that takes seriously the survival of political communities — and of humanity itself.

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August 1945: A Foundational Turning Point

In October 2025, Donald Trump’s announcement that the United States would resume nuclear testing —after more than three decades of de facto moratorium— signaled that nuclear capability was again being staged as a visible marker of status and resolve, not merely as a silent deterrent. Presented as a conditional response to possible Russian and Chinese tests, this declaration reactivated competitive logics of technological demonstration and raised immediate alarms among international verification and monitoring bodies such as the Comprehensive Nuclear-Test-Ban Treaty Organization, which warned of the cumulative erosion of arms control norms and the symbolic crossing of a threshold that many states considered politically and morally closed. In this renewed nuclear climate, the memory of Hiroshima and Nagasaki returns, not as a distant episode but as a living fault line in the international order. On 6 and 9 August 1945, the U.S. bombings of Hiroshima and Nagasaki inaugurated the nuclear age by combining, in a single act, military innovation, total destruction, and political signalling. Since then, historians, strategists, and philosophers have debated whether Truman’s choice was the least catastrophic option available or an avoidable moral catastrophe rationalized after the fact. Detailed archival work and revisionist interpretations confront each other: some emphasize the anticipated casualties of a land invasion and the pressure to end the war swiftly; others stress diplomatic alternatives, the looming Soviet entry into the conflict, and the desire to shape the post-war balance of power in Asia (Walker 2016; Alperovitz 1996; Maddox 1995; Bernstein 1995). The result is not consensus, but a structured disagreement that already contains the central problem of nuclear morality: whether extreme necessity can ever legitimize deliberately targeting civilians.

This unresolved tension reverberates in the twenty-first century, where nuclear discourse has re-emerged at the heart of crises in Europe and Asia. The war in Ukraine has been accompanied by explicit and implicit nuclear threats from Moscow calibrated to deter NATO involvement and freeze territorial gains; debates in Washington, Moscow, Beijing, Paris, London, and New Delhi revisit the vocabulary of “credibility,” “red lines,” and “escalation dominance,” as analyzed in contemporary deterrence and risk studies such as those of leading strategic institutes. Against this background, Nina Tannenwald’s concept of the “nuclear taboo” is crucial: she shows how, since 1945, a strong normative inhibition has developed against nuclear use, embedded in state practice, legal argument, and public discourse, and interacting with—but not reducible to—deterrence logics (Tannenwald 2007; Tannenwald 1999). Hiroshima and Nagasaki thus function as a strategic and moral mirror: they oblige today’s decision-makers to confront the link between historical memory, legal obligations, and the practical conditions under which the nuclear threshold might, or might not, hold.

Truman at an Impasse: Alternatives and Calculations – Military Urgency and the Limits of Strategic Rationality

By the summer of 1945, the Pacific War had become a prolonged catastrophe for Japan and a mounting burden for the United States, yet Tokyo showed no clear sign of unconditional surrender. Massive incendiary raids had devastated major cities; the naval blockade strangled imports of food and fuel; industrial capacity eroded; and yet the imperial leadership clung to the hope of extracting better terms or exploiting divisions among the Allies. The Japanese high command prepared Operation Ketsu-Go, a last-ditch defense of the home islands founded on near-total mobilization, suicide tactics, and the expectation that inflicting intolerable casualties on invading U.S. forces might shift American political calculations (Frank 1999). In Washington, planners faced a strategic impasse: defeat Japan decisively, but at what cost and by which means, in a context where domestic expectations demanded rapid victory and minimal additional bloodshed after V-E Day.

The first option, Operation Downfall, envisaged a two-stage invasion: Olympic against Kyūshū, followed by Coronet against Honshū and the Tokyo Plain. Intelligence assessments, informed by bitter experience at Iwo Jima and Okinawa, projected levels of resistance ranging from ferocious to apocalyptic. Some estimates anticipated hundreds of thousands of U.S. casualties; others, assuming mass mobilization and kamikaze tactics, reached the scale of one million (Giangreco 2009). Coupled with potential Japanese military and civilian deaths on an even greater scale, these projections placed Truman in front of a foreseeable slaughter that would be hard to justify politically to a war-weary American public. The specter of writing letters to hundreds of thousands of new bereaved families weighed heavily, reinforcing receptiveness to any option that promised to end the war quickly.

The second option, intensified blockade and continued conventional bombing, rested on the assumption that Japan, already economically prostrated, would eventually capitulate under the cumulative effects of famine, infrastructural collapse, and psychological exhaustion. In practice, this meant accepting months— perhaps more than a year —of additional suffering, with the likely death of millions of civilians from hunger and disease while the imperial regime clung to power (Maddox 1995). For U.S. leaders, this path looked less dramatic militarily but morally troubling and politically uncertain; it postponed peace and risked eroding support at home and unity among Allies.

A third option, championed by some Manhattan Project scientists and diplomats, was a technical demonstration: an atomic explosion on an uninhabited site, under international observation, preceded by a clear ultimatum to Japan (Alperovitz 1996). The idea promised to preserve some moral restraint while showcasing overwhelming technological superiority. Yet the fear of technical failure or reduced psychological impact, combined with doubts about Japanese leaders’ willingness to surrender without concrete devastation, led to its rejection. Truman and his advisers judged that a failed demonstration would embolden the enemy and weaken U.S. leverage vis-à-vis both........

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