Why South Korea Shouldn’t Build Its Own Nuclear Bombs
Are nuclear weapons the answer to Seoul’s security challenges? Amidst a flurry of North Korean nuclear-capable missile testing and persistent stresses in the U.S.-South Korean security alliance, conservative candidates in South Korea’s presidential primaries have called on the United States to redeploy tactical nuclear weapons to the Korean Peninsula. Some have even argued that South Korea should “independently seek nuclear armament” if the United States does not agree to redeploy. These views found support from two American academics, Jennifer Lind and Daryl Press, who contend in a provocative Washington Post op-ed that South Korean nuclear weapons may be “the only way” to save the alliance. Arguing for allied proliferation is a highly unusual policy prescription. In contrast, we believe that South Korean nuclear acquisition would be counterproductive and dangerous, leaving both the alliance and South Korean security worse off.
Lind and Press posit that South Korea is stuck between a rock and hard place, “pulled apart by powerful geopolitical forces.” For Seoul, joining U.S.-led regional security initiatives risks alienating China, South Korea’s closest trade partner. Yet, resisting U.S. demands to more effectively counterbalance China could threaten the reliability of U.S. protection. Moreover, the authors suggest North Korea’s improving ability to target U.S. cities with nuclear weapons challenges the credibility of U.S. commitments to come to Seoul’s aid in an inter-Korean conflict. The best course to resolve these dilemmas, according to Lind and Press, might be a South Korean nuclear arsenal, one they argue should enjoy U.S. political support.
Although the U.S.-South Korean alliance does face significant geopolitical challenges, nuclear proliferation would be an ill-advised solution. South Korean nuclear weapons would likely make the regional security situation more precarious. Moreover, alliance credibility problems have not reached a magnitude that calls for such a drastic measure. Instead, strengthening cohesion within the U.S.-South Korean alliance through non-nuclear means offers a viable — and safer — path to address regional challenges from North Korea and China.
The China Problem
South Korean leaders understand their regional security environment, including the mounting threats from China and North Korea and the centrifugal forces these create in the U.S.-South Korean alliance. China’s increasingly aggressive security policy toward its near abroad and its willingness to use economic coercion pose distinct threats for Seoul. Indeed, South Korean officials keenly recall the painful Chinese unofficial sanctions after Seoul agreed to host the U.S. Terminal High-Altitude Area Defense missile defense system in 2017 that cost the South Korean economy an estimated $7.5 billion in losses.
Understandably, South Korea has resisted U.S. overtures to join the Quad initiative with Australia, India, and Japan in order to avoid provoking more Chinese retaliation. Clearly, Seoul does not desire a “new Cold War” with Beijing, and it will encourage steps to prevent that outcome. Yet, in practice, South Korea’s efforts to strengthen relationships in Southeast Asia and with India through a “New Southern Policy” demonstrate it is contributing to U.S. counterbalancing initiatives, albeit in indirect ways. The May 2021 summit between Presidents Moon Jae-in and Joe Biden also affirmed a shared vision for how the alliance extends beyond the Korean Peninsula, including by “maintaining an inclusive, free, and open Indo-Pacific.” Remarkably, the summit statement also emphasized “the importance of preserving peace and stability in the Taiwan Strait.”
Thus, in both words and actions, South Korea is actively working with, and complementing, the United States to contend with the China problem. China may yet become a more direct threat to South Korea in the future, such that an independent South Korean nuclear arsenal or nuclear sharing arrangement with the United States might become more relevant. For the foreseeable future, though, the allies appear quite capable of managing the China problem in ways that meet their respective interests without requiring nuclear weapons to keep the alliance together.
An Alliance Credibility Deficit?
Lind and Press also point to alliance credibility challenges as a reason why South Korea should build its own nuclear weapons. They are certainly not alone in warning that U.S. nuclear credibility may be crumbling, yet there is plenty of evidence indicating the political and military foundations of the U.S.-South Korean defense relationship remain strong. Recent public opinion surveys by the Chicago Council for Global Affairs showed that 62 percent of Americans support the use of U.S. military forces to defend South Korea against a North Korean attack. This is matched by attitudes in South Korea, where the public also continues to express high levels of support for, and confidence in, the alliance. A September 2021 Asan Institute poll, for example, showed 78 percent support for maintaining or strengthening the U.S.-South Korean alliance.
Proponents of a South Korean nuclear weapons program argue, however, that South Koreans are no longer confident in the United States — they point to high levels of public support for nuclear proliferation (70 percent in the recent Asan poll) and concerns that South Korea’s military alone is not sufficient to deter North Korea (72 percent, according to Asan). But deeper research paints a more nuanced picture of the credibility challenge. For example, research by Lauren Sukin found that, in 2019, 58 percent of South Korean survey respondents believed the United States would use nuclear weapons to defend South Korea from a North Korean nuclear attack. Other work shows robust U.S. public support for the nuclear security guarantee to South Korea. Scholars have similarly found that the U.S. public is willing to use nuclear weapons, including against North Korea, and even when there is a high risk of nuclear retaliation. So the claim by Lind and Press that “South Korea can’t be sure it can depend on its U.S. ally for protection” seems overblown.
This is not to argue that concerns about alliance credibility have no basis. Building confidence in the alliance among the South Korean public is an ongoing challenge, made much harder in the wake of the Trump administration’s extortionate approach to alliance burden-sharing negotiations. South Koreans were also alarmed in 2017 that President Donald Trump’s “fire and fury” might result in a war they did not want. Yet, neither of these are problems are fundamentally about the reliability of U.S. promises to aid South Korea in a security crisis. Rather, they point to a need for better alliance political and military cohesion, especially coordination about contingencies involving North Korea that could escalate to use of nuclear weapons. In sum, alliance credibility problems are real but not as severe as many have suggested, and nuclear weapons are far from a clear remedy for the problems that persist.
Would Nuclear Weapons Improve South Korean Security?
Even if the alliance problems were as profound as some analysts contend — and if South Korean nuclear proliferation did not somehow make them worse — a South Korean decision to acquire nuclear weapons would not necessarily improve Seoul’s security against North Korea or China, as advocates have claimed. Indeed, a lot would depend on how North Korea and China would react to South Korean proliferation.
South Korean nuclear weapons may not be especially useful politico-military tools against China. U.S. nuclear threats against China during the Korean War did not dissuade Beijing from continuing to fight. Nor has China hesitated to leverage its conventional military strength in territorial contests with nuclear-armed India. China’s ongoing modernization of its nuclear forces — whether by constructing missile silos or testing hypersonics — suggests Beijing may view the survivability and effectiveness of its arsenal as vital for deterring the United States, especially in the Taiwan Strait. Would South Korean nuclear weapons dissuade Beijing from undertaking coercive operations against Seoul? It seems unlikely. If anything, South Korean proliferation could plausibly invite more coercive Chinese economic and military pressures if Beijing interpreted Seoul’s nuclear arsenal as a direct challenge to its regional aspirations. Vis-à-vis China, then, South Korea could wind up counterintuitively less secure with nuclear weapons than without them.
South Korean nuclear weapons could similarly make the situation with North Korea much more dangerous. Already, joint U.S.-South Korean military exercises, which Pyongyang calls “exercises for a nuclear war,” have repeatedly prompted North Korea to issue aggressive rhetoric, engage in cross-border provocations, and conduct missile tests. In the face of a South Korean nuclear weapons program, it would be unreasonable to expect North Korea to take no countervailing actions. For example, it seems likely that South Korean proliferation could cause North Korea to further augment its nuclear arsenal, posture its nuclear weapons for first use, or take greater risks to gain the upper hand in an escalating military crisis. After all, even the United States, with its far superior nuclear arsenal, has had limited success deterring or compelling North Korea.
Moreover, even if South Korean nuclear weapons likely would deter large-scale violence by China or North Korea, they could make the threat of low-level conflict escalation greater than it already is today. This is especially important in the Indo-Pacific context, where the most prevalent threats and sources of crisis escalation — such as China’s overflights of contested territory or North Korea’s offensive use of cyber capabilities — exist far below the nuclear threshold. The “stability-instability paradox” of nuclear weapons suggests that, although mutual possession of nuclear weapons may reduce the chances of nuclear war, it may, at the same time, make conventional wars and militarized crises more likely, as well as incentivize greater risk taking at lower levels. A more moderated version of this argument suggests that nuclear weapons may not necessarily make low-level conflict more likely, but neither do they prevent it.
For instance, a nuclear-armed South Korea could be emboldened to respond more aggressively to North Korean provocations with proactive deterrence or “quid pro quo plus” military operations, the inherent escalation risks of which are intended to dissuade North Korea in the first place. Facing perceived “use or lose” pressures, North Korea may be quicker to cross certain escalation thresholds, such as the use of long-range rocket systems, as it seeks escalation dominance. The potential for these action-reaction dynamics to spiral into a race up the escalation ladder is clear. To be certain, this potential is already present, but it seems likely to worsen if South Korea possessed nuclear weapons. Reaction times during moments of crisis would be shorter, tensions higher; miscommunication and misperception easier, and nuclear use more accessible. South Korean proliferation could, then, make conflict more likely at worst and fail to deter it at best.
Alternatives to South Korean Nuclear Weapons
Before South Korean leaders opt to acquire nuclear weapons, they should weigh these potential risks against the putative deterrence benefits proliferation proponents claim. In our assessment, leaning into nuclear deterrence as the corrective for regional security challenges, as some experts have advocated, is likely to be counterproductive. This approach positions nuclear weapons — incorrectly — as the best solution to regional tensions, in turn making proliferation look more appealing. Prioritizing nuclear solutions to the primarily non-nuclear threats South Korea and the United States face also exacerbates the extended deterrence credibility challenges for Washington. The United States would simultaneously have to prove it is ready to use nuclear weapons in a broad range of contingencies, while also conveying it is appropriately restrained such that it would not drag South Korea into an unwanted conflict. The latter point is particularly important as the Biden administration seeks to mend damaged alliance relations in the wake of the Trump administration.
Rather than expand the role of nuclear weapons in addressing threats from China and North Korea — or, as Lind and Press suggest, accept the inevitability of South Korean nuclear proliferation in response to these threats — the United States and South Korea should focus on making the alliance more resilient to the types of conflict escalation scenarios that are most likely to occur. Prioritizing political and military cohesion makes a North Korean “wedging” strategy — intended to break apart the U.S.-South Korean alliance — less likely to succeed, while also creating more avenues to satisfy Washington’s interests in engaging Seoul in broader regional security efforts. Peacetime consultations, improved crisis communications, and exercises intended to bolster military interoperability would all contribute to alliance reassurance, while improving military readiness for a variety of crisis situations. The alliance should especially prepare for threats below the nuclear threshold, including by planning for gray zone contingencies and adapting to new and emerging threats, like those posed by cyber operations.
One important avenue for strengthening alliance cohesion involves greater U.S. support to South Korea’s development of conventional counterforce capabilities and strategies. A conventional counterforce strategy relies on accurate, secure, and sufficiently impactful conventional forces for damage-limiting first-strikes and secure and punitive second strikes. In the last decade, and especially under the Moon administration, South Korea has invested considerable sums in developing very precise ballistic and cruise missiles to deter and respond to North Korea’s potential use of nuclear weapons. According to two senior South Korean military officers, Seoul’s acquisition of conventional counterforce capabilities “raises the expected costs of North Korea’s nuclear provocations and reduces the possibility of it achieving the desired political and military goals through the use of nuclear weapons.”
From this perspective, the ongoing military developments in South Korea may be less harbingers of nuclear proliferation than evidence that Seoul is developing a serious non-nuclear approach to regional security. U.S. efforts to reduce the risk of nuclear conflict — whether through arms control, crisis management exercises, or improved interoperability in support of South Korean conventional counterforce options — could strengthen the alliance, stabilize the Peninsula, and reduce proliferation pressures.
Lauren Sukin is a Ph.D. candidate at Stanford University’s department of political science and a pre-doctoral fellow at the Center for International Security and Cooperation.
Toby Dalton is a senior fellow at, and co-director of, the Nuclear Policy Program at the Carnegie Endowment for International Peace.