The structure of global security has been changing in profound ways. In Europe there is a major conventional war, and the potential for armed conflict seems to be increasing in other parts of the world including East Asia. The United States is no longer seen as a reliable security guarantor by its allies. 

One of the puzzling aspects of the global security architecture is that nuclear powers no longer seem to possess a coherent understanding of what their arsenals are for. Strategic capabilities are increasingly developed with conventional weapons, while nuclear deterrence fails to deter major conflict, a phenomenon that Rose Goettemoeller has referred to as “The Strange Defeat of Nuclear Deterrence.” This has the paradoxical consequence that regional powers feel the increasing need to acquire nuclear weapons. 

South Korea faces this dilemma very acutely. North Korea is increasing its nuclear arsenal and has developed a significant alliance with Russia even as Pyongyang has renounced unification and designated South Korea as its enemy. At the same time, the preparedness of the United States to defend its allies in the region has come into question. This is exacerbated by the fact that the continental United States is now within reach of North Korean ballistic missiles. 

The result has been an intense debate in South Korea about whether the country should acquire nuclear weapons. On July 27, retired Lieutenant General Chun In-bum published an article in the Korea Times that elaborated on a sophisticated proposal for South Korea to acquire a nuclear weapons arsenal, which Seoul would own but which would be imbedded in an integrated network of deterrence with the United States. This would resemble some of the deployments of nuclear weapons in Europe in the early Cold War, with a dual-key system that would require the consent of the host country and the United States for weapons to be launched. Chun admitted that this would raise significant issues with regard to the Nuclear Non-Proliferation Treaty (NPT), verification, and decision-making. 

Public surveys in South Korea have shown up to 80 percent support for South Korea acquiring a nuclear weapons capability. Among South Korean policy elites, there is less enthusiasm due to the potential consequences for the alliance with the United States, South Korea’s adherence to the NPT, and the economic implications. Policymakers tend to prefer a “threshold capacity” whereby South Korea would have the capability to quickly develop nuclear weapons but would not actually do so while the alliance with the U.S. remains in place. 

Strengthening nuclear deterrence on the Korean Peninsula can take several forms. One possibility would be to redeploy U.S. nuclear weapons in South Korea with the purpose of signalling to North Korea, China, and Russia that extended deterrence is serious. In Europe, the deployment of U.S. nuclear weapons was accompanied by the development of independent nuclear deterrents by Britain and France. But these nuclear arsenals were developed in a different environment when the strategic conflict with the Soviet Union was at the core of global security. The United States was unable to prevent the development of these independent arsenals and therefore chose to integrate them into its posture on European security. 

All of the proposed variants face the dilemma of “entrapment or abandonment.” Countries hosting U.S. nuclear weapons do not want a nuclear conflict to start without their consent, but they want extended deterrence to be effective. Likewise, the United States does not want to be embroiled in a nuclear conflict initiated by an ally. The fundamental dilemma is how to make nuclear deterrence credible to the adversary while balancing the risks in a manner acceptable to all parties. 

The problem with Chun’s proposed scheme is that it does not resolve this fundamental dilemma. If the United States maintains escalation control, this amounts to a veto in a different form. If South Korea had independent launch authority, then the United States could find itself  in a nuclear conflict against its will. It is really unclear therefore whether the implementation of Chun’s proposal or anything similar would solve the underlying problem.

South Korea’s negotiations with the United States over the transfer of wartime operational control (OPCON) over ROK forces – a process that has dragged on for two decades – illustrate the practical difficulties of such arrangements. OPCON transition requires highly coordinated intelligence and communication systems, interoperability, training, and finely tuned relations between South Korean and American commanders. Nuclear decision-making would be more complex and would have to include the U.S. president, but given the geography of the battlefield, decision times could be extraordinarily short. It would require substantial reassurance that there would be no unauthorized launch but the threat of retaliation would have to be credible to the adversary.

A South Korean nuclear arsenal, even if embedded in an alliance command structure, could complicate the regional security environment. It could encourage Russia to enhance its support of North Korea and its sharing of technology with respect to nuclear delivery and control systems. Beijing would be likely to consider such a capability as a threat to its own security. The decision to deploy the ballistic missile defense system THAAD in South Korea in 2016 provoked a major reaction from China with the imposition of political and economic costs. Then-South Korean President Moon Jae-in managed to partly assuage China by promising no further deployments of THAAD batteries and no integration into a region-wide U.S. led missile defense network. 

A South Korean nuclear arsenal is likely to provoke an even more serious reaction, including economic sanctions, increasing military deployments and potentially the deployment or retargeting of Chinese nuclear forces against South Korea. It could also rekindle the nuclear debate in Japan and lead to further nuclear proliferation. 

It is hard to predict how North Korea would react to a South Korean nuclear arsenal. It is true that deterrence of a North Korean nuclear attack would be enhanced. At the same time, it could provoke even more acceleration of North Korea’s efforts to develop a secure nuclear capability that could also strike the United States. It would not necessarily inhibit low-level attacks below the threshold of direct armed conflict. 

It would also change the narrative of a democratic South Korea acting in conformity with international law versus a rogue North Korean state if South Korea were to abandon its commitments to the Nuclear Non-Proliferation Treaty. Leaving the NPT is not just a reputational or technical issue. While South Korea would no longer be obliged to forego the manufacture or possession of nuclear weapons,  the United States would be constrained under Article I of the NPT not to transfer possession or control over nuclear weapons to South Korea or provide any nuclear assistance. The civil nuclear technology cooperation between the United States and  South Korea – the “123 Agreement” of 2015 – would be in jeopardy.

There is little immediate prospect that Chun’s ideas can become policy. But that does not mean that there are no paths forward. The integration of U.S. nuclear weapons and conventional forces into operational planning, nuclear consultation, integration of early warning, intelligence, missile defense, and various signals regarding the commitment to extended deterrence and no tolerance of North Korea aggression could strengthen stability. 

If South Korea feels it can no longer rely on the United States, then it could develop its own nuclear deterrent. But it would have to face the consequences, which may include  international isolation, severe strains on (or even the collapse of) the South Korea-U.S. alliance, and a more hostile international security environment.