Why U.S. Allies in Asia Are Chasing Nuclear Energy—And Eyeing Nuclear Weapons

Even more developed countries, like Japan and South Korea, are being affected by the energy crisis. Although Japan has significant strategic reserves, and both countries can temporarily switch to coal or purchase some LNG on the expensive spot market, leaders in Tokyo and Seoul are well aware that the situation could worsen quickly if U.S. President Donald Trump escalates by acting on his bellicose Easter comments. The crisis is now speeding up a debate within Japan and South Korea about expanding the use of nuclear power. In South Korea, there has also been renewed pressure to secure the rights to enrich a higher percentage of its own uranium for its nuclear plants. The Trump administration’s devotion of massive military resources to the Middle East—which has even diverted parts of the high-altitude missile interceptor system promised to South Korea—and its seeming indifference to Washington’s Asian allies has also sparked serious consideration in Tokyo and Seoul about whether the two Northeast Asian powers need their own nuclear weapons.

Even the possibility that South Korea could enrich a greater percentage of its own uranium would have massive geopolitical ramifications in the region. And if Japan and South Korea were to move toward becoming nuclear-armed states, the geopolitical shock—and danger—would be immeasurable.

South Korea is already one of the world’s largest producers of nuclear energy and is expanding its civilian nuclear capacity. Japan’s leadership, meanwhile, has made nuclear energy central to its policy agenda, despite lingering public concern from the 2011 Fukushima disaster. The Iran war has only accelerated Tokyo’s plans to reopen nuclear plants and build new ones.

South Korea’s 1974 nuclear deal with the United States, the so-called 123 Agreement, prohibited it from enriching its own uranium and required it to import enriched fuel instead. Late last year, Washington and Seoul agreed to a change that allows South Korea to enrich uranium up to 20 percent for civilian purposes. (This is far below weapons-grade levels of enrichment.)

The possibility of higher enrichment in South Korea has already led to severe warnings from the nuclear-armed North and from China. North Korea’s state news agency warned that South Korean domestic uranium enrichment, backed by the United States, was “laying a springboard for its development into the ‘quasi-nuclear weapons state.’” Beijing, too, has cautioned Seoul that even domestic enrichment for civilian nuclear energy could have consequences. China has not declared what these might be, but they could range from intense economic coercion—China is South Korea’s largest trading partner—to more aggressive Chinese military escalation, particularly in waters near South Korea.

For its part, Japan already possesses the capacity and right to enrich its own uranium. Without declaring it, Japan has what is called nuclear latency—the ability to rapidly develop nuclear weapons without actually crossing the threshold of building them.

As Daniel Sneider, non-resident fellow at the Korea Economic Institute (KEI), recently wrote in a column, Japan “has a stockpile of forty-five tons of weapons-grade plutonium (eight tons of it held in Japan), the capability to enrich uranium, ballistic-missile technologies developed under its satellite-launch programs, and advanced fighter aircraft with nuclear delivery potential. A recent report by the International Atomic Energy Agency observed that Japan’s latency hedges against regional threats while simultaneously functioning as diplomatic leverage against the United States should the Trump administration withdraw its security guarantees.”

Many South Koreans want the same capabilities as Japan, as they no longer trust the U.S. nuclear umbrella. Leaders in both countries have not only pushed for greater nuclear power but also increasingly raised the possibility of obtaining nuclear weapons.

Roughly 76 percent of South Koreans want to have an “indigenous nuclear weapons capability,” according to an April 2025 poll by the respected Asan Institute for Policy Studies—the highest figure Asan has recorded. In the same poll, less than half the respondents believed the United States would use nuclear weapons to defend South Korea if North Korea struck it with nukes. Former South Korean President Yoon Suk-yeol already set a precedent in 2023 by suggesting that South Korea could need nuclear weapons to defend itself.

With nuclear latency, either country could assemble weapons relatively quickly. Experts expect that this could take just a few months for Japan, but South Korea would likely take longer.

If South Korea were to attempt to achieve the kind of nuclear latency Japan possesses, it could theoretically make Seoul a regional pariah, lead to economic sanctions, or prompt the United States to formally withdraw its security guarantees, multiple experts on proliferation told me in interviews. And they suggest that the Asan poll should be taken with a grain of salt. Public sentiment in South Korea for indigenous nuclear weapons capacity softens significantly if people polled believe that shift would end the country’s alliance with the United States.

Still, Trump has at times suggested he might not stand in the way of allies in Northeast Asia obtaining nuclear weapons, and he seems far from concerned about regional proliferation. If Trump maintains this posture as South Korea pursues nuclear latency, Seoul would be less of a pariah and unlikely to face sanctions—though it would not reduce any geopolitical risk. Indeed, given that Beijing has offered dire warnings just about Seoul gaining greater enrichment capabilities, it is hard to determine how severely, and quickly, China could escalate a response if South Korea were to obtain nuclear latency.

As for Japan, moving closer to obtaining nuclear weapons would cause potentially even greater blowback from China, at a time when the two powers already face deteriorating relations. Chinese rhetoric on Japan’s Taiwan position hints at how Beijing might respond to Tokyo openly considering getting nuclear weapons. One Chinese state news outlet already called for Beijing to consider nuclear strikes on Japan just because Japan’s prime minister suggested that the country could become involved in a conflict over Taiwan.  

Yet Washington’s ambivalence toward nonproliferation in Asia and uncertainty about U.S. commitment to allies—a sentiment clearly felt in Europe, too, as France and the United Kingdom explore expanding their own nuclear umbrellas—could lead both Japan and South Korea to follow a path toward nuclear energy and, possibly, nuclear weapons. Former Lieutenant General Noboru Yamaguchi, a senior government advisor in Japan, told KEI’s Sneider: “It is impossible to prove extended [U.S. nuclear] deterrence is valid… Deterrence is about how we feel. It was questionable during the Cold War. Now I don’t believe in any kind of deterrence.”

Indeed, Japanese Prime Minister Takaichi Sanae, who just led her party to a massive electoral victory, has left open the possibility that Tokyo will abandon its commitment to not obtaining nuclear weapons. As the Carnegie Endowment’s Shizuka Kuramitsu notes, the prime minister has committed to “making ‘important policy shifts,’ including amending the Japanese Constitution. The election result may have also boosted her confidence to revisit the three non-nuclear principles.“

With Washington focused on the Middle East, the world desperate for energy, and Asian allies unsure of the future, the possibility of multiple nuclear-armed states in Northeast Asia looks dangerously plausible.

This work represents the views and opinions solely of the author. The Council on Foreign Relations is an independent, nonpartisan membership organization, think tank, and publisher, and takes no institutional positions on matters of policy.