The simplest explanation for why dropping nuclear bombs on Japanese cities was not considered a war crime in 1945 is that the people dropping the bombs were the same people defining the rules. The United States and its Allies controlled the legal framework, wrote the postwar tribunals, and shaped the narrative of what constituted lawful conduct. Hiroshima was not prosecuted as a war crime because the laws of war at the time did not prohibit bombing cities, no rules existed regarding nuclear weapons, the Allies themselves had normalized mass incendiary bombing, and the U.S. framed the attack as militarily necessary. Under the legal standards of 1945, the bombings fit within the accepted logic of total war.
Americans often hear more about Hiroshima than Nagasaki, perhaps because Hiroshima is easier to justify within the simplified narrative that “two bombs ended the war.” But the historical reality is far more complex. The United States originally planned to drop three atomic bombs on Japan and had a production schedule for ongoing nuclear strikes as soon as each bomb became available. Manhattan Project records show that Little Boy was dropped on Hiroshima on August 6, Fat Man on Nagasaki on August 9, and a third Fat Man–type bomb was scheduled for August 19. General Leslie Groves and General Thomas Farrell confirmed that the third bomb’s core was already being assembled. If Japan had not surrendered, the United States planned to drop it as soon as weather and delivery crews allowed.
A Planned Nuclear Campaign, Not Two Isolated Events
Hiroshima and Nagasaki were not intended as isolated events. They were meant to be the opening phase of a sustained nuclear bombing campaign. The Manhattan Project’s production pipeline was designed to deliver one bomb every 8–10 days through late summer 1945, increasing to two per month by autumn, and even more once Hanford’s plutonium reactors reached full output. The original target committee listed Hiroshima, Kokura, Niigata, Nagasaki, and Kyoto — removed only because Secretary of War Henry Stimson insisted. If Japan had not surrendered, Kokura was next, with Niigata also on deck. We might not have wiped Japan off the map, but anything less would be useless for decades.
The Human Toll: What the Bombs Actually Did
The human toll of the bombings was staggering. In Hiroshima, 70,000–80,000 people were killed instantly, most from blast, thermal radiation, or collapsing wooden homes. By the end of 1945, the death toll reached roughly 140,000, including radiation sickness, burns, infections, and delayed injuries. Thousands more died in the late 1940s and 1950s from leukemia, solid cancers, chronic radiation effects, and long-term organ damage. Around 70,000 people were injured.
In Nagasaki, 40,000–45,000 were killed instantly, with the Urakami Valley devastated despite the terrain limiting the blast. By the end of 1945, the death toll reached about 70,000, with thousands more dying in subsequent years from radiation-related cancers, chronic illness, organ failure, and long-term trauma. Roughly 60,000 were injured.
Casualty numbers vary because many victims were incinerated beyond recognition, Japanese wartime records were destroyed, early U.S. estimates undercounted radiation deaths, and later epidemiological studies revised totals upward. The consensus among historians is approximately 140,000 deaths in Hiroshima and 70,000 in Nagasaki by the end of 1945 — figures that represent only the first five months, not the decades of radiation-related mortality that followed. Those bombs didn’t create the largest death toll in Japan in a day. That record belongs to the Tokyo firebombing five months earlier. Find those in a high school textbook.
Why the Bombings Were Legal Then
Neither bombing was considered a war crime because bombing cities with defensive capabilities was legal, and atomic bombs — newly invented — were not on any list of prohibited weapons under the 1925 Geneva Protocol, which banned asphyxiating gas, poison gas, and bacteriological methods of warfare. The Hague Convention of 1899 prohibited expanding “dum-dum” bullets, poisonous gas projectiles, and balloon-launched explosives, but nothing in international law addressed nuclear weapons or the mass firebombing of cities. In short, the rulebook simply did not contemplate the technology that arrived in August 1945.
Why Hiroshima and Nagasaki Would Be Considered War Crimes TodayA Completely Different Legal Landscape
Under modern international law, the atomic bombings of Hiroshima and Nagasaki would almost certainly be classified as war crimes, and likely crimes against humanity, because the legal framework governing warfare has transformed dramatically since 1945. The most important shift is the development of International Humanitarian Law (IHL) after World War II, especially the 1949 Geneva Conventions, the 1977 Additional Protocols, and the evolution of customary international law. These frameworks place strict limits on how states may conduct war, especially regarding civilian protection, proportionality, and the use of indiscriminate weapons.
Indiscriminate Destruction: A Clear Violation Today
Modern law prohibits indiscriminate attacks and the use of any weapon or tactic that cannot distinguish between combatants and civilians. Nuclear weapons, by their nature, obliterate everything within a blast radius, ignite firestorms, and produce radiation that spreads far beyond any military target. The International Committee of the Red Cross has repeatedly stated that nuclear weapons violate the principles of distinction and proportionality because their effects cannot be contained. Hiroshima and Nagasaki were both cities with civilian populations far exceeding military ones, and the bombs killed tens of thousands instantly, mostly civilians. Under modern law, this alone would constitute an indiscriminate attack.
Radiation as “Unnecessary Suffering”
Modern law also prohibits weapons that cause superfluous injury or unnecessary suffering. Radiation poisoning — slow organ failure, leukemia, chronic cancers, genetic damage — fits squarely within this category. Survivors of Hiroshima and Nagasaki suffered long-term radiation effects for decades, including birth defects in subsequent generations. The Additional Protocols explicitly forbid weapons that cause long-lasting environmental devastation or lingering harm to civilian populations. Nuclear weapons are the textbook example of such harm.
Proportionality and the Question of Military Necessity
Even if one accepts the argument that the bombs shortened the war, the scale of civilian casualties — over 200,000 dead by the end of 1945 — would be considered disproportionate under contemporary standards. The fact that the U.S. planned to drop additional bombs every 8–10 days underscores that the strategy was not narrowly tailored to a specific military objective but part of a broader campaign of coercion through mass destruction.
The Prohibition on Terrorizing Civilians
Modern law prohibits collective punishment and attacks intended to terrorize civilian populations. The atomic bombings were explicitly designed to shock Japan into surrender by demonstrating overwhelming destructive power. Today, such intent would violate prohibitions on terrorizing civilians, which are codified in the Additional Protocols and recognized in customary international law.
The Modern Ban on Nuclear Weapons
Finally, the Treaty on the Prohibition of Nuclear Weapons (2017) — ratified by more than 90 countries — declares nuclear weapons illegal under international law. While major nuclear powers have not signed it, the treaty reflects a global consensus that nuclear weapons are incompatible with humanitarian principles.
The Bottom Line
Hiroshima and Nagasaki were not considered war crimes in 1945 because the legal framework was primitive, incomplete, and written by the victors. Under today’s laws — built from the ashes of the very destruction those bombs caused — the atomic bombings would be unequivocally illegal. One last thing to keep in mind: the bombing of Nagasaki was completely unnecessary. Japan was already negotiating its surrender. The only reason I can think of to go ahead with the bombing was to see which type of nuclear bomb was more powerful for use in the future. Sounds like a war crime to me.