In recent years, speculation among analysts, experts, and scholars that America’s two key allies in the Indo-Pacific could finally pursue nuclear weapons has intensified. The eminent diplomat Henry Kissinger predicted in 2023 that Japan would go nuclear within the decade. The international relations scholar John Mearsheimer has made the point that nuclearization by Seoul and Tokyo would be the “logical outcome” if the United States were to continue being distracted by conflicts in the Middle East. Washington Post columnist Max Boot has argued that the increasingly uncertain credibility of the U.S. nuclear umbrella should prompt South Korea to seek its own nuclear deterrent.

Their conjecture is neither surprising nor unprecedented. In the 1970s, for example, South Korea tried unsuccessfully to develop a covert nuclear program in response to concerns about U.S. abandonment. And the security environment has rarely been so uncertain for Seoul and Tokyo as it is today. Both countries face growing nuclear threats. China is in the middle of a major nuclear buildup, having more than doubled its arsenal in the last five years, with some estimates suggesting that Beijing could amass over 1,000 nuclear weapons by 2030. In 2023, Russia deployed tactical nuclear weapons outside its borders for the first time since the collapse of the Soviet Union, and Russian President Vladimir Putin amended the country’s nuclear doctrine in 2024, lowering Moscow’s threshold for nuclear use. North Korea is thought to have 50 nuclear weapons and enough fissile material for 50 more, and technical support from Russia is accelerating its development of a broad suite of mobile-launched, nuclear-tipped cruise and ballistic missiles, as well as nuclear submarines. Meanwhile, U.S. President Donald Trump has demanded that South Korea and Japan do more for their own security and has redeployed Patriot missiles and THAAD systems from South Korea and U.S. Marines from Japan to the Middle East because of the war with Iran.

A growing chorus of influential voices in Seoul and Tokyo seems to lend credence to the worry that this confluence of threats will prompt South Korea and Japan to cross the nuclear Rubicon. In 2023, South Korean President Yoon Suk-yeol mused that his country “could rapidly develop its own nuclear weapons” if the threat from North Korea continued to grow. Foreign Minister Cho Tae-yul stated in February 2025 that nuclear armament was “not off the table.” Later that year, a comment by an unnamed senior government official advising Japanese Prime Minister Sanae Takaichi expressing the personal opinion that the country should acquire the bomb sparked widespread public criticism—but some politicians, including former defense minister Taro Kono, argued that Japan should not shy away from a broader debate about the pros and cons of nuclearization. These statements are not inconsistent with public opinion. Polling in South Korea shows support for nuclear armament as high as 75 to 80 percent.In Japan, support for the country’s three non-nuclear principles—to not possess or produce nuclear weapons or allow them to enter Japanese territory—remains strong, but over 56 percent of Japanese........

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