Illustrations by Michael Haddad
Keiko Ogura was just 8 years old when the atoms in the Hiroshima bomb started splitting. When we met in January, some 300 feet from where the bomb struck, Ogura was 87. She stands about five feet tall in heels, and although she has slowed down some in her old age, she moves confidently, in tiny, shuffling steps. She twice waved away my offered arm as we walked the uneven surfaces of the Hiroshima Peace Memorial Park, first neutrally and then with some irritation.
Ogura can still remember that terrible morning in August, 80 years ago. Her older brother, who later died of cancer from radiation, was on a hilltop north of the city when the Enola Gay made its approach. He saw it shining small and silver in the clear blue sky.
Ogura was playing on a road near her house; her father had kept her home from school. “He had a sense of foreboding,” she told me. She remembers the intensity of the bomb’s white flash, the “demon light,” in the words of one survivor. The shock wave that followed had the force of a typhoon, Ogura said. It threw her to the ground and she lost consciousness—for how long, she still doesn’t know.
Like many people who felt the bomb’s power that day, Ogura assumed that it must have been dropped directly on top of her. In fact, she was a mile and a half away from the explosion’s center. Tens of thousands of people were closer. The great waves of heat and infrared light that roared outward killed hundreds of Ogura’s classmates immediately. More than 20,000 children were killed by the bomb.
Ogura told me that after the initial explosion, fires had raged through the city for many hours. Survivors compared the flame-filled streets to medieval Buddhist scroll paintings of hell. When Ogura awoke on the road, the smoke overhead was so thick that she thought night had fallen. She stumbled back to her house and found it half-destroyed, but still standing. People with skin peeling off their bodies were limping toward her from the city center. Ogura’s family well was still functional, and so she began handing out glasses of water. Two people died while drinking it, right in front of her. A black rain began to fall. Each of its droplets was shot through with radiation, having traveled down through the mushroom cloud’s remnants. It stained Ogura’s skin charcoal gray.
In the days following the bombing, Ogura’s father cremated hundreds of people at a nearby park. The city itself seemed to have disappeared, she said. In aerial shots, downtown Hiroshima’s grid was reduced to a pale outline. More than 60,000 structures had been destroyed. One of the few that remained upright was a domed building made of stone. It still stands today, not far from where Ogura and I met. The government has reinforced its skeletal structure, in a bid to preserve it forever. Circling the building, I could see in through the bomb-blasted walls, to piles of rubble inside.
Ogura and I walked to a monumental arch at the center of the Peace Memorial Park, where a stone chest holds a register of every person who is known to have been killed by the Hiroshima bomb. To date, it contains more than 340,000 names. Only a portion of them died in the blast’s immediate aftermath. Tens of thousands of others perished from radiation sickness in the following months, or from rare cancers years later. Every generation alive at the time was affected, even the newest: Babies who were still in their mothers’ wombs when the bomb hit developed microcephaly. For decades, whenever one of Ogura’s relatives took ill, she worried that a radiation-related disease had finally come for them, and often, one had.
As time passed, news that more countries had built nuclear arsenals reached Japan. Meanwhile, the hibakusha—the Japanese term for survivors of the nuclear attacks—were stigmatized as mutants. Ogura told me that girls in her summer camp looked for burn scars on her body in the shower. Some of her friends’ weddings were called off by prospective grooms who feared that birth defects would affect their future children. Ogura worried that her own wedding would be canceled right up until the ceremony.
Since the Hiroshima attack, Ogura and her fellow hibakusha have told and retold their stories of the bombing and its long aftermath. But even the youngest of them are now in their 80s, and soon they’ll all be gone. The horrific reality of an atomic attack is fading out of living memory—even as a new turn toward rapid nuclear armament makes the possibility of a full-blown nuclear war more likely.
For all the recent focus on Iran, in a cruel irony, East Asia is where the world’s fastest buildups are unfolding, in China and North Korea. A dangerous proliferation cascade may be about to break out, right in the shadow of Hiroshima. It would likely start in South Korea, and spread first to Japan. It might not stop there. The decades-long effort to keep nuclear weapons from spreading across the planet may be about to collapse.
One cold, windy morning in Seoul, a week before I met Ogura, I surrendered my phone at the gates of the Korea Institute for Defense Analyses, a government brain trust that advises South Korea’s Joint Chiefs of Staff. Inside the gray brutalist building, the nuclear strategist Heo Tae-keun was waiting for me. Heo had recently served as South Korea’s deputy defense minister for policy. In that role, he had led the country’s delegations in nuclear talks with the United States. He is a former brigadier general with a rugby player’s build, a sturdy presence in every sense. And yet, that morning, he seemed deeply troubled.
President Donald Trump had just begun his second term, but already he was showing less restraint than in his first. Almost immediately, he had threatened Denmark with military force, and he seemed content—delighted, even—to let Russia decide Ukraine’s fate. His disdain for old alliances unsettled Heo. “I am not sure what will happen in Trump 2.0,” he told me. In Korea, he said, in the cautious way of a diplomat, “he is perceived as more unstable in his decision making” than previous U.S. presidents.
Stability is prized by nuclear strategists, who by dint of their profession have had to envision, with disturbing vividness, what instability looks like in the nuclear realm. As America’s dependability as an ally comes into question, Heo, like many other South Koreans, is looking around nervously at the dangerous neighborhood where his country is located. South Korea hangs like an earlobe off the eastern edge of Eurasia. Not even a tiny moat like the Taiwan Strait separates it from the three nuclear-armed autocracies immediately to its north. The first of them, North Korea, is still technically at war with South Korea, and Seoul’s 9 million residents are attuned to its closeness. From the city center, where skyscrapers stand alongside old palaces preserved since the Joseon dynasty, it takes just 40 minutes to reach the thin strip of land-mine-riddled wilderness that separates the two countries.
When North Koreans came pouring over the border at the start of the Korean War, in 1950, both peoples were poor, and still suffering the aftereffects of Japan’s brutal 35-year occupation. Then, for three years, that war raged up and down the peninsula, from snowy ridge to snowy ridge, killing more than 2 million people. Heo told me, laconically, that South Koreans have no desire to repeat that experience. He gestured toward the sleek, gleaming city outside his window. “We overcame the Korean War, and built an economy and way of life,” he said. North Korea has less to lose.
Kim Jong Un has ruled as dictator in Pyongyang for 13 years, during which he has often threatened the South with reunification by force, and, more recently, outright annexation, just as Vladimir Putin has attempted in Ukraine. Kim is quickly expanding his nuclear arsenal. He already has dozens of warheads, and has threatened to use them not only as defensive weapons of last resort, but in a first strike that would turn Seoul into a “sea of flames.”
For decades, the threat of intense U.S. retaliation helped keep Kim’s father and grandfather from invading the South. But Kim rules at a time when Pax Americana looks to be winding down. Under Trump, the United States is now reported to be considering pulling troops out of South Korea, though administration officials have denied that. “The Korean people do not know if the U.S. commitment to them is real,” Heo told me. They may soon decide that to deter Kim, they need nuclear weapons of their own.
For the better part of a century, the U.S. has sought to limit nuclear proliferation, with considerable success. American presidents have deployed diplomats, saboteurs, and brute military force to stamp out nascent nuclear-weapons programs in Latin America, Europe, Africa, and Asia. They have done so because nuclear weapons are dangerous, and because each new nuclear nation further dilutes the awesome power that America had when it was the only one.
Just once has the U.S. helped an ally start a nuclear-weapons program, by sharing technical research with the United Kingdom, its junior partner on the Manhattan Project. In 1946, Congress outlawed all such sharing, and in the decades since, U.S. presidents have worked to keep West Germany, Australia, Libya, Brazil, Sweden, and others from building arsenals—and even helped persuade South Africa to dismantle an arsenal that it had already built. Today, of the world’s 193 countries, only nine have nuclear weapons.
Left to its own devices, South Korea could easily have been the tenth. The country is wealthy and technologically adept, and with North Korea next door, it has sufficient motive. The reason the South Koreans don’t yet have an arsenal on hand is that both times they started to build one, an American president found out and persuaded them to stop.
The military junta that ruled South Korea in the 1970s launched the country’s first covert nuclear program after the U.S. signaled a pullback from Asia that would culminate in the fall of Saigon. The nervous generals were secretly negotiating with France to purchase a reprocessing plant. When Gerald Ford found out, his administration threatened to terminate the U.S.-Korean military alliance, and pushed to cancel the sale. In the end, South Korea ratified the Nuclear Non-Proliferation Treaty instead, in 1975.
Only six years later, after North Korea broke ground on a plutonium reactor, Ronald Reagan’s administration intervened to halt another such program. It was less serious than the first, but Reagan still wanted it canceled: He assured Chun Doo-hwan, South Korea’s president at the time, that U.S. ground troops would remain on the Korean peninsula indefinitely, and Chun agreed to shut weapons research down for good.
North Korea has not seen fit to restrain its nuclear ambitions in the same way. During the heady years after the Cold War, George H. W. Bush removed the American warheads that had long been stationed at bases in South Korea, then pressured its president to sign a joint pledge with North Korea to keep the peninsula forever free of nuclear weapons. That pledge proved to be a sham; North Korea tested its first crude nuclear device just 14 years later, during George W. Bush’s presidency.
Barack Obama, an optimist on all matters nuclear, believed that he could persuade China to lean on North Korea until it gave up its nuclear program. This didn’t work either. Chinese leader Xi Jinping’s first priority regarding North Korea was and is the stability of Kim’s regime: If Kim’s rule collapses, refugees will flood into China and Xi will lose the buffer state that separates it from South Korea, America’s longtime ally. Xi’s willingness to press was limited, and so Kim kept on building warheads.
Xi may feel, in any case, that he is in no position to lecture Kim about proliferation. He himself is engaged in the fastest warhead buildup undertaken by any country since the Cold War’s peak. For decades, China was fine with having a few hundred warheads on hand as a deterrent. But Xi is now adding about 100 a year. He wants an arsenal as large as the ones that the U.S. and Russia have, if not larger. It’s part of his Chinese Dream, the great rejuvenation that he has imagined for his country.
And so, in some sense, a destabilizing proliferation cascade has already begun in East Asia, and proliferation often begets proliferation. Julian Gewirtz, who served as the senior director for China and Taiwan affairs on the National Security Council during the Biden administration, told me that China’s astonishingly fast and ambitious nuclear buildup has unsettled countries all across Asia. In both South Korea and Japan, he said, these concerns, combined with uncertainties about the Trump administration, “may lead them to consider ideas that were once unthinkable.”
Kim is already estimated to have about 50 warheads, and the material needed to build as many as 90 more. His nuclear ambitions have grown along with China’s. He doesn’t want to be a nuclear peer of India and Pakistan, who have contented themselves with about 170 warheads each. Kim wants to have about 300, like the United Kingdom and France, sources told me.
Heo said that nuclear strategists have developed some notions about how Kim might use an arsenal of 300 warheads if nuclear war were to ever break out on the peninsula. The first 100 of them would likely be reserved for Kim’s short-range missiles. They would be able to reach targets in South Korea—military bases, airfields, ports, and perhaps even Seoul itself—in less than two minutes. The radius of the attack could then move beyond South Korea, with another 100 warheads available to strike the country’s regional allies, Japan in particular. Kim is trying to build reliable intercontinental ballistic missiles, onto which the remaining 100 warheads would be fastened. They could be launched all the way to the United States, in waves, to overwhelm missile defenses.
North Korea’s first ICBM test, in 2017, was a “threshold breaker,” Jake Sullivan, who served as national security adviser under Joe Biden, told me. It showed that Kim’s effort to build missiles that could reach the U.S. mainland was further along than previously thought. He may now be getting help from Russia, in exchange for the 14,000 troops and millions of rounds of ammunition that he has sent to Ukraine. If Kim could plausibly put Washington, D.C., or Los Angeles in existential jeopardy, would the U.S. really protect Busan and Seoul?
This is the question that haunts Heo. He knows that American presidents have a lot of wiggle room when it comes to protecting South Korea. The mutual-defense treaty between the two countries is vague. When President Dwight Eisenhower negotiated it, South Korea’s leaders were still eager to restart the Korean War, to defeat the North once and for all. Eisenhower was willing to station nuclear weapons in South Korea to reassure them, but he refused to promise American military support in every case of conflict between the two countries, because he feared that the South would deliberately provoke a war.
The U.S. has always been cagey about its nuclear contingency plans for the region. Even after North Korea acquired nuclear weapons, when Americans conducted tabletop exercises with South Korea, they would often end them just after North Korea launches its first missile, which is right when things get interesting, from the South Korean point of view. The United States Strategic Command, which operates America’s nuclear-weapons systems, doesn’t like to divulge its contingency plans. The South Koreans tend to “leak like a sieve, and their systems have been penetrated by the Chinese,” a former senior Pentagon official told me. STRATCOM officials have professed not to understand why South Korea should even require reassurance; their attitude was Our word has been good for decades, and it’s still good—just take it.
As Trump first rose to power, South Koreans found it more difficult to just take America at its word. In 2016, they watched in horror as he riled up rally crowds by denigrating America’s Asian allies as freeloaders. Trump said that South Korea and Japan were ripping off the U.S. in trade and sending only “peanuts” in exchange for an American military presence in the region. He seemed to take special pleasure in threatening to draw down, or perhaps even wholly remove, the nearly 30,000 troops stationed in South Korea.
During his first presidency, Trump flattered Kim, and flew to meet the North Korean dictator at summits in Hanoi and Singapore. In exchange for this sheen of legitimacy, Kim paused his missile tests, but only for a couple of years, during which he reportedly kept adding to his nuclear stockpile. A reminder of Trump’s failed policy can still be glimpsed from a border lookout point north of Seoul. When I visited it in January, I could see a pale-gray building a mile or so into the demilitarized zone, beyond wild bush and barbed wire. Trump and Kim met there in 2019, but since then, it has stood mostly vacant, a potent symbol of America’s newly unpredictable foreign policy.
According to opinion polls conducted in recent years, 70 percent of the South Korean public wants the country to have its own nuclear arsenal. In 2022, voters elected the conservative Yoon Suk-yeol, a hawk’s hawk on North Korea, to the presidency. Mira Rapp-Hooper, who served as the senior director for East Asia and Oceania on Biden’s National Security Council, told me that she and other officials grew concerned during Yoon’s campaign when he called for the return of tactical U.S. weapons to the Korean peninsula. After Yoon assumed power, the Biden administration tried to reassure him that no such arsenal was necessary. Biden’s staff proposed a grand gesture, a declaration that would serve as an addendum to the two countries’ vague mutual-defense treaty.
The Washington Declaration was announced during Yoon’s visit to the White House in April 2023. That night, at a state dinner held in Yoon’s honor, he and Biden clinked glasses to celebrate the 70th anniversary of the alliance. Yoon, who is not otherwise known for his personal charm, rose to the occasion, singing a few bars of “American Pie,” by Don McLean, in English, to loud cheers from the assembled guests. A few months later, an American Ohio-class nuclear submarine docked in Busan, as a show of strength. But by then, Biden’s presidency, and its policy of reassurance, was close to an end. Over the course of the following year, it became clearer that Trump would be his successor. For the second time in less than a decade, Americans would elect as their leader a chaotic and untrustworthy man who seemed hostile to the very concept of alliances.
When Heo and I discussed the possibility that South Korea may need to go nuclear, he emphasized that he wouldn’t want an arsenal just for its own sake. Members of the defense intelligentsia would prefer to keep the American alliance the way it is. But they have to prepare, in case South Korea is left to deal with Kim on its own. Like almost everyone I talked with in Seoul, Heo eventually mentioned Ukraine. When the Soviet Union fell, Ukraine had a nuclear arsenal on its soil, but Bill Clinton helped persuade the Ukrainians to give it up. Not to worry, he said. The U.S. will have your back.
Near the end of my time in Seoul, I sat down to lunch with Park Jin, who served as foreign minister under Yoon. We met at a café downtown, just as the morning’s snowfall was letting up. Park, 68, has the elegant manners that you might expect of a former top diplomat, and he was stylishly dressed in a black blazer and turtleneck, set off by a gray cashmere scarf. Just a few days earlier, in the hours following Trump’s inauguration, the new president had offhandedly referred to North Korea as a “nuclear power” in response to a reporter’s question about foreign threats. Park was focused on that remark. He told me he had initially hoped that it was a simple mistake, but those hopes were dashed when Trump’s incoming defense secretary, Pete Hegseth, used the same language in a written statement to the U.S. Senate.
This characterization may sound innocuous, given that everyone already knows that North Korea has a nuclear arsenal. But official recognition of a rogue nuclear power is usually a prize to be bargained for in geopolitics. It was not one that any previous American president had been willing to grant Kim, and certainly not for free. Park believes that Trump was using it as a concession to lure Kim to another meeting, one that could hasten his country’s abandonment by America. “The North Korea issue is the unfinished business from his first administration,” Park said. “And he’s a businessman.”
Having already conceded North Korea’s legitimacy as a nuclear power, Trump won’t have many cards to play if he does attempt another renegotiation with Kim. Now that Kim’s nuclear arsenal is larger and Russia is his ally, he has more leverage, and may not even wish to meet. In search of a deal, Trump might try to secure a commitment from Kim to stop building ICBMs that threaten the U.S., and then declare victory—leaving North Korea’s ability to nuke Seoul entirely intact. Several South Korean security elites told me that a deal like that would be tantamount to abandonment, especially if it were paired with a troop withdrawal.
During his first term, Trump asked his staff to set a troop withdrawal from South Korea in motion. James Mattis, his secretary of defense, reportedly slow-walked the request. Now, according to The Wall Street Journal, the Defense Department is reviewing its Korea policy, and a reduction in troops is being considered, although a Pentagon spokesperson denied that there was any “immediate” plan to draw down forces.
If Trump does try again to withdraw troops from South Korea, it’s not clear what would stop him. When Jimmy Carter attempted something similar, he was foiled by intelligence assessments that counseled strongly against it. But Tulsi Gabbard, Trump’s director of national intelligence, is an isolationist, and—like the rest of his Cabinet members—a loyalist above all else. She has already fired agents for an inconvenient intelligence assessment. She could make sure that no one stands in Trump’s way.
It can sometimes be helpful to think of there being two South Koreas. The country is highly, and maybe even dangerously, polarized. The month before I arrived in Seoul, Yoon had declared martial law on false pretenses. Shortly after I landed there, he was charged with insurrection. Walking the streets, I heard dueling mass protests, for and against him. A megaphone call-and-response boomed through the downtown high-rises. In early June, Lee Jae-myung, a liberal candidate, won the snap election to replace Yoon. Normally, the election of a liberal president would quell talk of a South Korean nuclear-weapons program for a while, but now even some of the country’s liberals are nuclear-curious. In March, two foreign-policy-establishment figures from the new president’s party said that it is time to consider nuclear armament.
Months before Trump’s reelection, Victor Cha, the Korea chair and president of geopolitics at the Center for Strategic and International Studies, sent a survey to hundreds of South Korea’s national-security elites. Of the 175 that responded, 34 percent said that they were in favor of South Korea acquiring its own nuclear weapons. But that poll is already out-of-date. The nuclear conversation among South Koreans has only grown louder since Inauguration Day, and Cha expects the volume to rise even more in the coming years. If a pro-nuclear consensus took hold among elites, it could all move quickly, because public support is already there, Cha told me.
I heard something similar when I visited Yang Uk, a nuclear strategist at the Asan Institute for Policy Studies, in Seoul. After giving me a tour of his office—a charmingly boyish space packed with model fighter jets and combat knives in glass cases—Yang told me that he, too, has been hearing more nuclear talk among South Korean strategists, and not only within the small clique that has long supported a homegrown nuclear program. It’s happening among lots of mainstream people, he said.
If South Korea were to launch a nuclear program, it would probably do so in secret. Its leaders would want to avoid suffering through an American-led sanctions regime, as India did after detonating nuclear devices in 1998. South Korea’s export economy would shrink rapidly if Hyundai and Samsung suddenly couldn’t sell their cars, smartphones, and chips abroad. “We would be fucked,” Yang told me. He may have been speaking personally: The Asan Institute is funded by an heir to the Hyundai fortune.
South Korea might secretly seek America’s blessing. Cha imagined South Korea putting a feeler out to the White House: You don’t have to support our nuclear program. Just don’t oppose it. Some people in the current Trump administration wouldn’t be inclined to oppose it at all. During his 2016 campaign, Trump himself suggested that South Korea and Japan should consider getting their own nuclear weapons. Elbridge Colby, now his undersecretary of defense for policy at the Pentagon, has said that the U.S. shouldn’t use sanctions to deter Seoul from developing them. Colby has just been put in charge of formulating America’s National Defense Strategy.
I called Scott Kemp to ask him how quickly South Korea could spin up a plutonium weapon. Kemp, a professor at MIT, is an expert on the industrial mechanics of proliferation who previously counseled the U.S. government on questions of this sort. He told me that in a mad-dash scenario, South Korea would probably need only a year to reprocess enough nuclear waste from its power plants to make a weapon. “There are plutonium-bomb designs floating around,” he said. “It would astonish me if South Korea had not acquired some of them.”
To build out an entire arsenal that would present a clear deterrent to North Korea would take longer, perhaps 10 years. “Those would be 10 very dangerous years,” Cha told me. Many of the riskiest scenarios introduced by nuclear weapons arise during these unstable “breakout periods,” especially when adversaries are operating with limited information.
If Kim learned of the program, he might use force to try to prevent its success, as Israel has in Iran. Even if he did not use nuclear weapons, he might try to invade, especially if there were fewer U.S. troops in his way. South Korea would be able to marshal a much more capable military response than Iran, and if a war did break out, it could last years and possibly draw in the neighborhood nuclear powers. Russia would probably back Kim, and China might pitch in too. In 2016, Xi Jinping levied harsh sanctions on South Korea just for installing a single missile-defense system. Xi would be aghast to learn that a new nuclear arsenal was materializing just 250 miles from the Chinese mainland. News of a South Korean arsenal would be consequential throughout East Asia. It would almost certainly spur further proliferation in North Korea and China, but also quite possibly in Japan.
Late one night after arriving in Tokyo, I met Cha for a drink on the top floor of the Okura Hotel. Beneath us, the city’s elevated freeways curved through a dense matrix of glass towers, giving the Akasaka district its layered and futuristic feel. Cha was in town for a security summit; in a ballroom on a lower floor, he and I had just attended a private speech by Shigeru Ishiba, Japan’s prime minister. Less than a minute into the speech, Ishiba had mentioned the threat from North Korea. Cha noted that for all of this public North Korea talk, in private, it was the prospect of South Korea going nuclear that seemed to spook Japanese security experts the most.
Japan and South Korea have mutual-defense commitments, but they are not friends. Koreans have not yet forgiven Japan for devoting an entire bureaucracy to the sexual enslavement of Korean women during its violent colonization of the peninsula. Japanese elites will tell you that their leaders have apologized many times for these crimes, and even paid compensation. Korean elites will tell you that the compensation was paltry, and the apologies heavy on the passive voice. They note that Japan’s history textbooks still take quite a sympathetic view of its imperial adventures in Korea.
Both countries depend on America for their national security, and neither wants to be the junior partner in the region. South Koreans do not like that the U.S. allowed Japan to reprocess uranium into plutonium, starting in 1987, while they still cannot. Japan’s conservatives wonder why it was South Korea that received a special Washington Declaration and not their country. You can imagine how tempers in Tokyo would flare if South Korea were to leapfrog plutonium-rich Japan and develop nuclear weapons first.
I asked Ken Jimbo, one of Japan’s most respected nuclear strategists, what his country would do in that instance. We met in a conference room at the International House of Japan, overlooking the institute’s famous garden. Originally owned by a samurai clan, it had, unlike most local Edo-style gardens, survived the Allied firebombing of the city. The red-and-white Tokyo Tower loomed behind it in the eastern sky. Jimbo told me that if South Korea built its own nuclear arsenal, the desire to possess such weapons would surely spill over to Japan. “We would have to be very serious about what to do next,” he said.
Japan has been rearming itself with impressive speed already. As the country’s war crimes have receded in historical memory and China has grown stronger, many Japanese have come to feel that the country’s pacifist constitution is outmoded. Jimbo told me that he was personally embarrassed when the troops that Japan sent to Afghanistan in 2001 weren’t allowed to join combat missions. During the decade following the outbreak of that war, Prime Minister Shinzo Abe led a movement to loosen the constitution. The country’s militarization has recently accelerated: By 2027, its defense budget will have surged by 60 percent in just five years. There isn’t yet a loud, open conversation about going nuclear in Japan, as there is in South Korea. As the lone people on Earth to have suffered nuclear attacks, the Japanese have so far remained committed to three “non-nuclear principles,” which require the country not to produce nuclear weapons, possess them, or host others’ on Japanese soil. A generation ago, belief in these principles was so strong in Japan that it was hard to imagine the country ever building an arsenal.
But antinuclear sentiment has lost potency during the past 20 years, according to Masashi Murano, a senior fellow at the Hudson Institute. China’s rapid nuclear buildup has unnerved the public, Murano said, and so has North Korea’s. Japanese media once covered Kim’s family as an eccentric sideshow. Now every smartphone in the country gets a push alert when Kim lobs a missile into the Sea of Japan, or over the Japanese archipelago and into the Pacific.
I asked Narushige Michishita, a strategist and professor at the National Graduate Institute for Policy Studies, in Tokyo, if he could imagine the circumstances that would push Japan to go nuclear. He told me that he would pay close attention to what America’s president did. I asked what kinds of things he would watch for. A map of East Asia sat unfurled between us. Michishita touched his finger to South Korea and Taiwan. If the U.S. abandoned either of them during a crisis, Japan would probably need to go nuclear, he said.
Scott Kemp, the MIT professor, told me that Japan has almost certainly already done the preparatory work. In 1969, Prime Minister Eisaku Sato is said to have signed a secret memo, instructing the government to make sure that Japan would be ready to build a nuclear arsenal should the need arise. That same year, Sato’s administration began to put an enormous amount of money into its centrifuge program, which now reprocesses nuclear waste into plutonium. I asked Kemp how long Japan would need to make a single warhead. His answer: Only a month, if speed were of the essence.
Nuclear weapons can be thought of as a kind of cancer that started metastasizing through human civilization in 1945. A few times during the Cold War, this cancer threatened to kill off much of humanity, but a partial remission followed the fall of the Berlin Wall. The U.S. and the Soviet Union agreed on a limit of 6,000 deployed warheads each—still enough to destroy most of the world’s major cities many times over, but down from the tens of thousands that they’d previously stockpiled.
The high-water mark for the disarmament movement came in 2009, when President Obama called for a world without nuclear weapons. For this address, Obama chose Prague, the site of the Velvet Revolution. He cast his eyes over a crowd of thousands that morning, and then over the whole continent. Peace had come to Europe, he said. Now it was time to go further, and negotiate a new arms-control treaty with Russia. The very next year, the two countries committed to cap themselves at 1,550 deployed warheads. At the time, China still had fewer than 300. Disarmament wasn’t on the near horizon, but the trajectory was favorable.
How long ago that moment now seems. The world’s great-power rivalries have once again become fully inflamed. A year after invading Ukraine in 2022, Putin suspended his participation in the capping agreement with the United States. He has begun to make explicit nuclear threats, breaking a long-standing taboo. Meanwhile, the Chinese have slotted more than 100 ICBMs in deep desert silos near Mongolia. The military believes that the U.S. has to target these silos, and Russia’s silos, to deter both countries, and doing so eats up “a big chunk of our capped force,” the former senior official at the Pentagon told me. Nuclear strategists in both of America’s major parties are now pushing for a larger arsenal that could survive a simultaneous attack from Russia and China. Those two countries will likely respond by building still more weapons, and on the cycle goes.
The writer Kenzaburo Oe has argued that it is the Japanese—and not the American scientists at Los Alamos—who have most had to reckon with the possibility that all of these nuclear weapons could bring about our extinction, or something close to it. This national reckoning has a geography, and Hiroshima and Nagasaki are its sacred sites. The day before I met Keiko Ogura in the Peace Memorial Park, I rode the bullet train southwest from Tokyo past the snow-tipped cone of Mount Fuji, then Old Kyoto and Osaka’s outer sprawl. In the early afternoon, I arrived at Hiroshima station and made my way to prefecture headquarters to meet Hidehiko Yuzaki, governor of the Hiroshima prefecture.
Yuzaki’s warm cherrywood office is the size of a small apartment. He has been governor for more than 15 years, and in that time, he has become the global face of Hiroshima. He played a large part in the G7 meeting that the city hosted in 2023, and Obama’s official visit in 2016—the first by a sitting U.S. president. Yuzaki is sometimes criticized for what local rivals say is an excessive focus on international affairs, but he sees his work with foreign leaders as continuing a great tradition in Hiroshima, dating back to the second anniversary of the atomic attack on the city. The mayor at the time, Shinzo Hamai, organized a peace festival, and in a speech that afternoon, he argued that Hiroshima should take on a new role in global culture as a mecca for the contemplation of disarmament. Since then, the city has been rebuilt into a wholly modern metropolis, but also an open-air museum that forces the mind out of the abstract realm of grand strategy and into the concrete reality of nuclear war.
I asked Yuzaki if he has become disillusioned as the world has again tipped toward nuclear proliferation. Was he troubled that the fastest buildups are occurring in East Asia, in Hiroshima’s backyard? He told me that he was frustrated. It was disheartening to him that people hadn’t yet grasped the real meaning of nuclear weapons. So long as anyone has them, there is always a risk of proliferation cascades, and no one knows where this new local one may end. The desire for these weapons is contagious, and could spread well beyond nervous national-security types in Seoul and Tokyo.
Indeed, the entire Non-Proliferation Treaty regime could unravel altogether. When Israel, India, and Pakistan went nuclear, they were not part of the Non-Proliferation Treaty (nor are they today), but South Korea is a member in good standing and Japan is, in some sense, the treaty’s soul. If those two countries flout the agreement, it will have effectively dissolved. Jake Sullivan, the former U.S. national security adviser, told me that the risk of a global proliferation cascade would rise “considerably.” The initial regional cascades are easy to imagine. The American pullback in Ukraine has already made Poland and Germany a lot more interested in going nuclear. If the Iranian nuclear program survives Israel’s attacks and develops a weapon successfully, Saudi Arabia and Turkey will likely want arsenals as well. The number of countries that have nuclear arms could quickly double.
We have some muscle memory for how to manage nuclear rivalries among a few great powers, Sullivan told me. But a strategic landscape of 15 or 20 nuclear powers could be risky in ways that we cannot anticipate. The odds of a nuclear exchange occurring would rise. The most potent current warheads are more than 80 times as destructive as the bomb that leveled Hiroshima’s urban core, and they now fly on missiles that can reach their targets in mere minutes. It would take only one of them to all but erase Tokyo, Seoul, Beijing, or New York City. The total damage that even a limited exchange of these more powerful weapons would cause is mercifully unknown to us, but it may be vain to hope for a limited exchange. The most elaborate and significant war game in the literature suggests that the cycle of nuclear vengeance would continue until the arsenals of all involved parties are spent. If a nuclear conflict does someday break out, death and destruction might very quickly unfold on a planetary scale.
Every moment that humanity spends with these weapons spread across the Earth, pointed at one another, is a foolish gamble with the highest-possible stakes. We are betting every chip that our nuclear-weapons technology and alert systems will not malfunction in existentially dangerous ways, even though they already have, several times. We are betting that no head of state who has red-button access will descend into madness and start a nuclear war, even though we know that leaders run the whole gamut from Marcus Aurelius to Caligula.
Before I left the Hiroshima-prefecture headquarters, I asked Governor Yuzaki what people usually overlook when they come to his city. Yuzaki paused for a moment to consider the question. He has personally hosted heads of state who control these arsenals. He said that most people are moved. He has watched foreign dignitaries weep in Hiroshima’s museums. He has seen them sitting in stunned silence before the memorials in the Peace Park. People feel horrible about what happened here, he told me. But they don’t seem to understand that humanity is now risking something even more terrible. They think that Hiroshima is the past, Yuzaki said. It’s not. It’s the present.
This article appears in the August 2025 print edition with the headline “The New Arms Race.”
The post The New Nuclear Arms Race appeared first on The Atlantic.
