The moderates, meanwhile, were prepared to gamble that the Americans would retain the basic outlines of the imperial institution after the war and decided this was the best chance left of preserving a version of kokutai they could live with. Emperor Hirohito himself came to agree with the moderates, influenced in part by increasing worries over the fate of the imperial regalia—the three sacred relics, a mirror, curved jewel, and sword, whose possession legitimized his dynasty and symbolized its divine origin.

During the final week of the war, the moderates finally came to a position the Americans could accept, but the hardliners remained intransigent, and the Japanese government had no mechanism for breaking the deadlock. (Pro tip: never establish a decisionmaking body with an even number of participants.) What the atomic bombs and Soviet entry really did was give the emperor and his advisers an excuse to intervene in support of the moderates’ position. But the expression of that position in the Japanese note of August 10 was problematic because it was couched in the extreme rhetoric of the hardliners, thus almost defeating its purpose. Luckily for all involved, the Byrnes note of August 11 handled the issue delicately enough to set the stage for a second imperial intervention on August 14, which allowed the war to end relatively cleanly.

From Then to Now

The ultimate evolution of postwar Japan proved more successful than anyone in 1945 could have imagined. During the occupation, the Americans decided to retain the imperial structure while forcing major political reforms, paving the way for the emergence of a liberal democratic constitutional monarchy—one that has been peaceful, prosperous, and stable ever since. And as with politics, so too with security. For all the worries about impending Armageddon, including those expressed by the father of the bomb himself, the nuclear era has witnessed not devastating war but the longest great power peace in the history of the modern international system. 

At first, it wasn’t clear how nuclear weapons could be reconciled with normal geopolitics. Breaking the cycle of war seemed impossible. Continuing it seemed unthinkable. Tensions ratcheted up further when the Soviet Union got the bomb in 1949. And then, in June 1950, North Korean forces invaded South Korea. Washington and its allies quickly jumped in on Seoul’s side, facing off against Moscow, which along with Beijing was backing Pyongyang. The question of how would war play out in the nuclear age would finally be answered.

For three years, as brutal fighting raged up and down the Korean Peninsula, the two sides gradually felt each other out and tacitly settled on the rules of the road for the new epoch. Neither of the nuclear powers wanted another total war, so both put strict limits on the conflict’s means, ends, and scope. They chose not to use nuclear weapons. They chose not to attack each other’s territory or regime, keeping the fighting to the Koreas. And beyond that, the war was allowed to proceed conventionally, as viciously as the belligerents wanted. These rules weren’t arrived at through negotiations but evolved in practice. Nuclear weapons, for all their power—because of all their power—turned out to be surprisingly powerless. Using them would carry many costs and bring few benefits. It would create more problems than it solved. And so, neither superpower did it. 

A decade later, the Cuban Missile Crisis reinforced the growing taboo against nuclear use and left the parties still more risk averse. Then Vietnam followed the same pattern as Korea. None of the nuclear powers, now including China, used nuclear weapons. None attacked another nuclear power’s territory or regime. And beyond that, anything went. The same rules held in the Gulf War, the Iraq War, and the Soviet and American wars in Afghanistan. They held for conflicts involving nuclear powers elsewhere (apart from some minor skirmishing). And they are holding once again in Ukraine, despite widespread worries to the contrary. 

Oppenheimer ends with a chilling exchange in which the title character muses that he once thought the Manhattan Project might destroy the entire world, then concludes sadly, “I believe we did.” It remains possible that he could be proved right, and complacency would be a mistake. Nearly a quarter of the way through the twenty-first century, however, Churchill’s final take seems more prescient: “By a process of sublime irony [we] have reached a stage in this story where safety will be the sturdy child of terror, and survival the twin brother of annihilation. … The day may dawn when fair play, love for one’s fellow-men, respect for justice and freedom, will enable tormented generations to march forth serene and triumphant from the hideous epoch in which we have to dwell. Meanwhile, never flinch, never weary, never despair.”

Gideon Rose is the Mary & David Boies Distinguished Fellow at the Council on Foreign Relations and the author of How Wars End.

Image: Shutterstock.