Recent domestic public polling has once again drawn attention to the debate over nuclear armament in South Korea. Survey results released on February 21 by The Chicago Council on Global Affairs (CCGA) show that 71 per cent of South Korean citizens support the development of an indigenous nuclear capability, while 56 per cent support reintroducing US tactical nuclear weapons to South Korea. The Fall 2021 KINU Unification Survey similarly demonstrated that a growing majority of South Koreans support possessing nuclear weapons, but both research teams noted that support for nuclear armament fell when respondents were asked to choose between nuclear weapons and US forces in Korea. Nonetheless, North Korea’s accelerated buildup of military capabilities and uncertainties in the US-South Korea alliance have weakened confidence in US extended nuclear deterrence, leading some conservative politicians to renew calls for the redeployment of US tactical nuclear weapons to South Korea. Others have gone as far as to recommend that Seoul pursue its own domestic nuclear weapons programme. These sentiments and stressors are not new. Recent calls for nuclearisation fit into a broader history of a country that has attempted to covertly develop nuclear weapons and faces persistent regional security threats that make a nuclear capability look desirable to some.

In some ways, South Korea is already charting a path towards nuclearisation. In October 2021, Seoul successfully tested a submarine-launched ballistic missile (SLBM), becoming the first nuclear non-possessor state to test such a system. SLBMs are usually acquired by countries looking to secure a second strike nuclear capability. There are also plans to construct a small modular nuclear reactor at the Gampo atomic research complex for submarine propulsion—despite a US treaty that limits nuclear materials to civilian purposes. South Korea already has a high-level of nuclear latency, and deployment of reactors using highly enriched uranium (HEU) would only shorten the time necessary for it to develop a nuclear weapon. These developments have prompted speculation about Seoul’s potential nuclear ambitions.

Arguments in favour of proliferation are underpinned by a belief that North Korea will never give up its nuclear weapons, and concerns about the reliability of US extended nuclear deterrence in a potential conflict. In a Washington Post op-ed, two American academics made the case for proliferation on these grounds. Due to a “weakening” of the US-South Korea alliance and the two countries’ diverging regional security objectives, the authors argued that Seoul would be better off developing its own nuclear capabilities to hedge against the growing threat from Pyongyang. They suggest that the US should “render political support‘’ for such a move. Other analysts have rejected this proposal, and arguments in favour of nuclear proliferation are not mainstream in Washington. Still, given the mainstreaming of arguments for possession, it is important to understand what stressors might be motivating proposals for nuclearisation, consider ways to address Seoul’s defence insecurities, and mitigate the temptation to go nuclear.

Stressors

Recent developments have lent credence to calls for South Korea to pursue its own nuclear weapons programme. For one, former President Trump and his transactional view of alliances shook confidence in US defence commitments. Trump badgered Seoul over the cost of maintaining US troops in South Korea, and reportedly even threatened to withdraw them. Even President Biden has in in some ways exacerbated these concerns among traditional allies, irking close partners on Afghanistan and AUKUS.

Potential changes to the US nuclear doctrine are also at play. The Biden administration through its ongoing nuclear posture review floated adopting a ‘no first use’ policy, which would have drastically limited US ability to provide nuclear deterrence guarantees. Only after vehement protests from allies did the administration back down from considering “no first use.” However, the review is reportedly still leaving up for consideration a “sole purpose” policy, which would narrow the US nuclear use doctrine to circumstances such as a direct attack on the US or responding to a nuclear strike. Under such a policy, threats to US allies in the form of chemical or conventional weapons would be excluded from US extended nuclear deterrence. US allies such as South Korea and Germany, which depend on the nuclear umbrella as non-possessor states, oppose the proposed shift in policy.

Another concern is that the Pyongyang’s nuclear and missile advancements might make it more difficult for the US to intervene in a conflict on the Korean Peninsula. Since North Korea’s Intercontinental Ballistic Missiles (ICBMs) are now capable of striking major US cities, as is believed to be the case with the Hwasong-14 and 15, the risk to the US of retaliation in a conflict would be significantly higher. These are the sort of factors driving some to recommend that Seoul consider an individualistic approach to its own security through nuclearisation.

Bad Tradeoffs

Proposals recommending an indigenous bomb raise the question of whether South Korea’s security situation would actually be improved by such an acquisition. It is not certain what effect the development of South Korean nuclear capability would have on North Korea’s nuclear use decision-making. One worst-case possibility is that the prospect of a nuclear Seoul alone drives Pyongyang to the point of considering a preemptive strike. At minimum, the risks and costs of miscalculation and low-level conflict escalation on the Korean Peninsula would grow without any improvement in deterrence. North Korea has repeatedly demonstrated that it will not hesitate to cut-off vital bilateral communication lines over any perceived slight to the regime. A nuclear-armed South would increase the North’s paranoia in a situation where those risk management guardrails happened to be out-of-service. Moreover, if another “nuclear domino” falls in Asia, the opportunity cost of others becoming NPT breakout states would also be lowered. It’s easy to imagine a cascading proliferation effect in the region and an overall deteriorated security environment.  

Further, the US has never tolerated the idea of a nuclear South Korea, and Seoul pursuing nuclearisation would likely coincide with the virtual end of the US-South Korea alliance. Indeed, the arguments laid out in the Washington Post op-ed are predicated on the notion that the alliance with the US is at odds with South Korea’s security concerns, and imply a choice between the alliance and nuclear weapons. It’s a self-fulfilling prophecy where a major impetus for a South Korean nuclear deterrent is the supposed weakening of the alliance, yet efforts to develop such a capability would itself be a major challenge to the relationship.

Reintroducing nuclear weapons to South Korea would also amount to abandoning any potential diplomatic solution towards denuclearisation or peace on the Korean Peninsula. While the prospects of coaxing Pyongyang to denuclearise are dim at present, it would be much less inclined to do so down the road if giving up its nuclear weapons meant being at a disadvantage to a nuclear Seoul. South Korea walking out of the NPT will have disastrous consequences for the global non-proliferation regime, compounding the blow dealt by North Korea’s departure from the treaty in 2003 and providing further reason for Pyongyang to feel justified in possessing its own arsenal.  Opportunities to diplomatically pursue peace and denuclearisation with North Korea would likely fizzle out, delivering a huge blow to efforts towards regional peace and stability.

What may end up being the most powerful deterrent against efforts to procure an indigenous bomb is the economic and political isolation South Korea would incur as an NPT breakout state. The US generally levies sanctions against governments that engage in proliferation activities, and South Korea—while a less likely target as a traditional ally—could be subject to these if it goes down the nuclear path. As an export-oriented economy, Seoul would suffer huge losses if it were on the receiving end of economic sanctions responding to nuclear weapons development. If it was directly faced with the threat and reality of these consequences, much of the steam would be let out of proposals for nuclearisation.

KINU’s survey results demonstrated that at least at present, a plurality of the South Korean public values the alliance with the US more than it desires nuclear weapons. The Washington Post op-ed is right that the alliance faces challenges, and that Washington’s regional security objectives are not always in alignment with Seoul’s (particularly on China). But it would be far more productive to address those challenges together and strengthen the alliance rather than doomsday-prepping as if the alliance has already failed. The US should engage in low-cost alliance maintenance to inspire more confidence in its commitments to the relationship and demonstrate a higher prioritisation of Korean Peninsula security issues. This could include reaffirming commitments to extended deterrence and United States Forces Korea (USFK) through diplomatic visits and talks, collaborating on implementing conventional counterforce measures, actively engaging with North Korea on the prospective end-of-war declaration, and finding ways to improve strategic cohesion with South Korea on political and defence issues.

CCGA’s new research paints a more complex picture where non-security factors, such as the perceived global prestige conveyed by a nuclear weapons programme, may also be important in shaping attitudes among the South Korean public. If the results are confirmed, this may complicate efforts to steer Seoul off the nuclear path by strengthening US extended deterrence alone. The US should continue to message strongly on the consequences of nuclear proliferation and help South Korea pursue international prestige through other means.

Chris Gowe is a recent graduate of American University and a former research intern with the Asia-Pacific Leadership Network (APLN).