Introduction

 
The nuclear balance of power in Northeast Asia is in crisis. North Korea, China, and Russia are using their nuclear arsenals as cover to undermine the regional order. Meanwhile, South Korea and Japan must rely on the promise of U.S. extended nuclear deterrence commitments that can only be called upon in the event of nuclear war and which are otherwise ineffective at stopping the current nuclear arms race. Given the emerging Eurasian nuclear axis, it is time to explore similar collective countermeasures among U.S. allies. In the 1960s, the United States deployed over 2,000 non-strategic nuclear weapons, commonly known as tactical nuclear weapons, in both South Korea and Japan. This was to deter conventional military threats from China and North Korea, long before they had their own nuclear weapons, in addition to the Soviet Union. Now that there are three nuclear threats in Northeast Asia, it is time to restore the U.S. nuclear force posture to reflect the threats of the 2020s. The redeployment of U.S. tactical nuclear weapons to South Korea and Japan would represent a third way between the risky pursuit of an indigenous nuclear weapons capability by these countries and the current dependence on offshore U.S. strategic weapons.

Cold War Lessons and Commitments

 
The deployment of U.S. nuclear weapons in South Korea and Japan is not new. Beginning in the late 1950s, the United States began forward deploying nuclear weapons to its military bases in South Korea and Japan, as well as in Taiwan, the Philippines, and its overseas territories like Guam. These weapons were intended to deter North Korea and Communist China from conventional military provocations, as well as for use in the event of a global conflict against the Soviet Union. Crucially, these U.S. weapons were deployed years before Communist China tested its first nuclear weapon in 1964 and decades before North Korea acquired its own nuclear arsenal in the 1990s. At its peak in 1967, the United States had 3,200 nuclear weapons deployed in the Western Pacific, including 950 nuclear weapons in South Korea and almost 1,200 in Japan.¹ These weapons, along with the U.S. military presence, preserved the balance of power in Northeast Asia throughout the Cold War.

With the end of the Cold War, the United States and Russia accelerated their arms control efforts. In 1991, Russian President Mikhail Gorbachev withdrew 10,000 tactical nuclear weapons deployed in Europe, while U.S. President George H. W. Bush withdrew 1,200 tactical nuclear weapons deployed in the Pacific, including 100 from South Korea, under mutual agreement with President Gorbachev. To this day, the United States continues to deploy over 100 B61 nuclear gravity bombs at allied airfields across Europe, including in Belgium, Germany, Italy, the Netherlands, and Turkiye.²

The North Korean Nuclear Threat

 
Even as the United States withdrew its nuclear weapons from the Korean Peninsula, South Korea reaffirmed its non-nuclear commitments. It negotiated with North Korea to sign the Joint Declaration on the Denuclearization of the Korean Peninsula in December 1991. The Declaration stated that the two Koreas “shall not test, manufacture, produce, receive, possess, store, deploy or use nuclear weapons.” But North Korea broke its promises. Over the next 20 years, North Korea violated all of its non-nuclear commitments as it built a comprehensive nuclear arsenal. North Korea has continued to develop nuclear weapons in violation of numerous international and inter-Korean denuclearization agreements, including the 1970 NPT, the 1991 Joint Declaration, the 1994 U.S.- North Korea Geneva Agreed Framework, and the September 19, 2005 Six-Party Talks Joint Statement.

North Korea is now estimated to have already secured enough fissile material to manufacture at least 100 nuclear warheads. According to a joint report by the Asan Institute for Policy Studies and the RAND Corporation in 2023, North Korea could increase its nuclear fissile stockpile for up to 300 nuclear warheads by 2027.³ North Korean leader Kim Jong Un stated in January 2024 that he would “exponentially” increase the number of nuclear warheads, and revealed a uranium enrichment facility in September.⁴

North Korea has diversified not only its nuclear warheads but also the delivery means. Since North Korea’s nuclear program was discovered in the early 1990s, South Korea has been within the range of North Korea’s short- and medium-range ballistic missiles, including the Scud and the Rodong missiles. Japan also became a potential target of North Korea’s nuclear weapons since the mid-to-late 1990s when Rodong missiles with a maximum range of 1,300 km were deployed for operational use. North Korea has showcased various short- and medium-range nuclear-capable missiles. These include the KN-23 (North Korea’s version of the Russian Iskander SRBM), KN-24 (North Korea’s version of the U.S. ATACMS TBM), KN-25 (“super-large” SRBM), Haeil “Tsunami” (a nuclear-armed UUV), Hwasal “Arrow” (strategic cruise missile), and Pulhwasal “Fire Arrow” (submarine-launched cruise missile). Japan is also within the range of North Korea’s medium-range ballistic and cruise missiles, including the Hwasong-9 (Scud-Extended Range variant) and Hwasong-12.

The Eurasian Nuclear Axis

 
It is not only North Korea’s nuclear weapons that pose a threat to South Korea and Japan. In 1961, China and Russia each signed mutual defense treaties with North Korea that provided for military intervention. Russia signed the North Korea-Russia Treaty on Comprehensive Strategic Partnership in 2024 and the two countries are strengthening their alliance through North Korea’s 10,000-strong troop deployment in support of Russia’s invasion of Ukraine. Russia clearly signaled its nuclear intentions in February 2023 by declaring its withdrawal from the New Strategic Arms Reduction Treaty (New START), a U.S.-Russia nuclear arms reduction treaty. According to the Federation of American Scientists (FAS), Russia possesses 5,580 nuclear warheads as of 2024.⁵ Russia threatened to use nuclear weapons as part of its invasion of Ukraine and it has forward-deployed its own tactical nuclear weapons in Belarus.⁶

Meanwhile, China has begun an ambitious nuclear weapons modernization program of its own. It currently has 600 operational nuclear warheads in its stockpile which will grow to 1,000 by 2030, and it is also diversifying its nuclear delivery systems.⁷ In addition, there remain concerns about a potential Chinese attack against Taiwan that could involve the threat or use of nuclear weapons, similar to Russia’s threats against Ukraine, to deter the United States and its allies from coming to its defense.⁸

China and Russia no longer feel the need for the “complete denuclearization of the Korean Peninsula,” which they have nominally supported. Instead of trying to solve the North Korean nuclear issue, they now aid and abet North Korea’s illegal nuclear arsenal. Concerningly, China and Russia are signaling their collective nuclear strike capabilities by conducting combined bomber task force patrols through the East Sea between South Korea and Japan. These air patrols have included Chinese Xian H-6K bombers and Russian Tu-95MS Bear bombers, which are capable of carrying nuclear weapons.⁹ The so-called “CRINK” axis of China, Russia, Iran, and North Korea has emerged as a dangerous coalition of authoritarian regimes unafraid of using nuclear threats and coercion to achieve their strategic objectives.¹⁰

The opaque command and control authority in these authoritarian regimes makes their nuclear arsenals more dangerous than those possessed by democracies. North Korea has authorized the use of nuclear weapons at Kim Jong Un’s discretion by enacting the September 2022 “Nuclear Forces Policy Law.”¹¹ Russian President Putin approved a new nuclear doctrine in November 2024, which has significantly lowered the threshold for nuclear weapons use by stipulating that Russia could use nuclear weapons even in response to non-nuclear attacks if they pose a “threat to Russian sovereignty.”¹² His invasion of Ukraine is but the latest in a long history of unilateral military actions in which deterrence has failed to work. Chinese leader Xi Jinping’s unprecedented third leadership term and widespread purges of military leadership, including the People’s Liberation Army’s Rocket Force, suggest that he will continue to consolidate decision-making authority with his loyalists.¹³

The world has therefore been transformed from one in which nuclear weapons were once considered unusable to one in which their use is now a real possibility. A world in which the nuclear forces of Eurasia’s authoritarian regimes operate as one is a nightmare for South Korea, Japan, and the entire liberal international order. Their “nuclear shadow” is the cover for their attempted dismantling of the U.S. security commitment to its allies.¹⁴ In January 2025, the Bulletin of the Atomic Scientists moved its Doomsday Clock to 89 seconds to midnight, signaling that the world is the closest it has ever been to nuclear catastrophe.¹⁵

Shifting South Korean and Japanese Attitudes

 
Despite these trends, South Korea and Japan have consistently adhered to non-nuclear principles while relying on the U.S. nuclear umbrella as their ultimate security guarantee. Japan was attacked with nuclear weapons during the Second World War, but it is often forgotten that 40,000 Koreans working in Hiroshima and Nagasaki were also killed in the atomic bombings.¹⁶ Both peoples have suffered the devastation of nuclear war. In December 1967, Japanese Prime Minister Eisaku Sato clarified the Three Non-Nuclear Principles of “not possessing, not producing, and not permitting the introduction of nuclear weapons.”¹⁷ After briefly considering the option of nuclear armament in the face of U.S. abandonment during the 1970s, South Korea ratified the Nuclear Non-Proliferation Treaty (NPT) in April 1975 and Japan did so the following year in June 1976.¹⁸ South Korea and Japan embraced the peaceful use of nuclear energy, becoming pioneers in civil nuclear use and standard-bearers for non-proliferation standards.

While these non-nuclear principles are admirable, it would be an act of folly to remain defenselessly vulnerable to an adversary’s nuclear threats in order to uphold these principles. The global security environment is already very different from when the NPT regime was established in 1970. In fact, it is different even from when the two Koreas signed the Joint Declaration on the Denuclearization of the Korean Peninsula in December 1991. It is finally time for South Korea to terminate the 1991 inter-Korean Declaration.

South Korean and Japanese desire for stronger nuclear deterrence options stem from increasing threats but also uncertainty about U.S. extended deterrence commitments. This reassurance dilemma has intensified over the past decade due to President Donald Trump’s unorthodox approach to the Eurasian nuclear axis as well as traditional allies. President Trump has mentioned a “trilateral arms control initiative” with Russia and China as part of a grand détente.¹⁹ He has also frequently touted his personal rapport with Kim Jong Un and called North Korea a “nuclear power,” upending decades of bipartisan U.S. commitment to not recognize or legitimize North Korea’s nuclear program.²⁰ The risk of U.S.-North Korea “nuclear arms-control talks” cannot be ruled out, whereby sanctions on North Korea are partially lifted and U.S.- North Korea relations are normalized in exchange for a freeze on North Korea’s nuclear capabilities at a level that does not directly threaten the continental United States.

The South Korean and Japanese publics are increasingly open to considering stronger nuclear options. The Asan Institute’s public opinion surveys have found 66.3% support for the redeployment of nuclear weapons, a figure that stays above a majority even when pressed to consider potential costs.²¹ In Japan, according to a 2022 Mainichi Shimbun poll, 57% of respondents supported discussing nuclear sharing, compared to 32% who were against—nearly twice as many in favor of the discussion.²² In recent years, not only South Korean leaders but also some Japanese leaders have hinted at the need to revise longstanding assumptions around nuclear deterrence. For example, former Japanese Prime Minister Shinzo Abe reflected that “We should not put a taboo on discussions about the reality we face,” when it comes to nuclear-sharing.²³ Similarly, Japanese Prime Minister Shigeru Ishiba has stated that “The Asian version of NATO must also specifically consider America’s sharing of nuclear weapons or the introduction of nuclear weapons into the region.”²⁴

The Lesser of Two Evils

 
For some, indigenous nuclear armament might be the answer for South Korea and Japan to address nuclear threats. However, this risks inadvertently undermining the ROK-U.S. alliance and hastening U.S. abandonment, not to mention exposing South Korea to a self-help security situation that it is not yet militarily prepared for. For Japan, indigenous nuclear armament would be even harder. Rather than breaking with the United States by seeking indigenous nuclear weapons or repeating the same failed extended deterrence performance, South Korea and Japan should encourage the United States and the Trump administration to rethink deterrence in a collective manner. This can begin with a cost-benefit analysis of the infrastructure and operational costs for forward-deploying B61-12 gravity bombs to their previous locations at Kunsan Air Base in South Korea and Kadena Air Base in Okinawa, Japan.²⁵

If the United States needed over 2,000 nuclear weapons deployed in South Korea and Japan in 1967 to deter conventional aggression, there is a strong case that even a tiny fraction of that number should be considered in the face of the unprecedented nuclear threats in 2025.²⁶ Allies must be prepared to bear a higher burden by once again hosting nuclear weapons while the United States must be willing to share greater control and decision-making authority similar to its posture in Europe. Moreover, these weapons could eventually be withdrawn as part of any future arms control talks that make progress towards denuclearizing the Korean Peninsula, as originally agreed to by all parties three decades ago. Until then, an updated U.S.-led nuclear force posture that includes forward-deployed tactical nuclear weapons would be a visible and tangible demonstration of collective resolve that restores a balance against the Eurasian nuclear axis.