Last week, the United States and South Korea commemorated the seventieth anniversary of their security alliance. South Korean President Yoon Suk Yeol came to Washington for a state visit amid great pomp and circumstance. The visit was a prominent opportunity for the United States to reassure South Korea that, despite a fast intensifying North Korean nuclear threat on Seoul’s doorstep, the alliance would be up to the task of deterring North Korean attack, including the use of nuclear weapons.
To this end, Yoon and U.S. President Joe Biden unveiled the Washington Declaration, a bilateral assertion of the alliance’s evolution amid a changing security environment on the Korean Peninsula. As Biden noted, the declaration is meant to “reinforce extended deterrence and respond to” North Korea’s advancing nuclear threats. The declaration also includes an affirmation of South Korea’s existing nuclear nonproliferation commitments, serving as an implicit assurance that Seoul will remain a nonnuclear weapon state despite the surging calls for an independent nuclear capability in South Korea.
The Washington Declaration is best understood as a software upgrade for the U.S.-South Korea alliance. Despite growing calls for the redeployment of U.S. nuclear weapons to the Korean Peninsula, the declaration takes no steps in this direction—consistent with the Biden administration’s 2022 Nuclear Posture Review. Instead, it focuses on expanding the ambit of intra-alliance consultations on nuclear weapons matters and further integrates the forces of the United States and South Korea in ways that can limit unintended escalation and buttress deterrence.
First, the United States has committed to “make every effort to consult with the ROK on any possible nuclear weapons employment on the Korean Peninsula.” While there is no formal legal requirement for the United States to consult with allies prior to nuclear employment in their defense, this measure serves to politically reassure Seoul that, in a crisis, the U.S. president will seek input from his South Korean counterpart, who could similarly initiate consultations with Washington on nuclear weapons matters.
Second, the declaration announces the creation of a new Nuclear Consultation Group (NCG). Adding to the alphabet soup of existing alliance political consultations, the NCG will be a forum to discuss “nuclear and strategic planning.” As a supplement, the alliance also aims to incorporate new measures that will allow South Korea to plan to support U.S. nuclear operations with its conventional capabilities. The two sides will conduct new exercises and training to this end.
The NCG and plans for greater South Korean conventional integration with U.S. nuclear operations borrow heavily from analogous institutions and practices in NATO. NCG consultations, for instance, are likely to mirror NATO’s Nuclear Planning Group (NPG) and the U.S.-chaired High Level Group. In the bilateral U.S.-South Korea context, the NCG is likely to be duplicative of existing alliance consultations on U.S. nuclear capabilities and policies. Nevertheless, growing perceptions in South Korea that an NPG-like consultative body—ideally, one with “nuclear” in its very name—is needed in the current environment have led to the creation of the NCG. Over time, the NCG could serve as a template for a trilateral consultative mechanism including Japan, which would be a meaningfully new addition to U.S. extended deterrence consultations with its two treaty allies in Northeast Asia.
Third, the declaration opens the door to new types of U.S.-South Korea force integration in the context of the alliance. The most significant measure here—and one that will likely receive few headlines because it has little to do with nuclear weapons—is the declaration’s goal “to closely connect the capabilities and planning activities of the new ROK Strategic Command and the U.S.-ROK Combined Forces Command.” Better joint operational planning in this regard can reduce the chances of unintended escalation being driven by Seoul and Washington failing to act in lockstep during crises. As South Korea’s conventional deterrence capabilities grow ever more advanced and capable, ensuring intra-alliance integration will be key.
The Washington Declaration also notes that the alliance will seek new ways to support U.S. nuclear operations on and around the Korean Peninsula with South Korean conventional military support, though the nature of this cooperation is unspecific. This may include direct South Korean conventional support, including conventional missiles and air support, to potential U.S. nuclear operations. Another possibility is that the alliance will move toward NATO-like programs whereby South Korean fighters could support U.S. nuclear-capable bombers. While similar practices could be established in the U.S.-South Korea context, North Korea’s limited and largely obsolete air defense capabilities reduce the military salience of such exercises on the Korean Peninsula.
Fourth and finally, the declaration features reaffirmations of South Korea’s existing nonproliferation commitments. The declaration notes South Korea’s “commitment to its obligations under the Nuclear Nonproliferation Treaty as the cornerstone of the global nonproliferation regime,” as well as to an existing bilateral agreement. These reassurances are complementary to the measures discussed above and serve as a reminder of the nonproliferation function of U.S. extended deterrence.
The interwoven reassurances on extended deterrence and nonproliferation implicit in the Washington Declaration hearken back to the height of the Cold War, when the United States navigated similar dilemmas in Europe. For instance, the structural context of the Washington Declaration and Biden’s reassurance of Yoon is similar to then president Lyndon Johnson’s reassurance of West German chancellor Ludwig Erhard in 1965. At the time, a combination of new consultative mechanisms, forward-deployed nuclear weapons, and political reassurances prompted West Germany to turn away from the bomb and toward a sustained reliance on U.S. extended deterrence. Washington no doubt has hopes that Seoul will be similarly reassured by the Washington Declaration.
Historical analogies, however, are imperfect, and the Washington Declaration is already being met with skepticism among Seoul’s most ardent proponents of a domestic nuclear weapons program. Some nuclear proponents in Seoul—including some within the Yoon administration—may further interpret Washington’s willingness to meet South Korean demands on extended deterrence in the Washington Declaration as a direct result of their domestic advocacy. Yoon’s remarks in January that Seoul “could acquire our own nuke” alarmed U.S. officials, and the Washington Declaration’s adoption of new measures could create a moral hazard problem for the alliance where continued demands for nuclear reassurance persist.
The very enterprise of extended deterrence, however, requires that the United States keep managing allied insecurities. The task of allied reassurance is never complete, and allies are never entirely sated. When matters grow inevitably worse on the Korean Peninsula in the aftermath of a long-anticipated North Korean nuclear test or a full-range intercontinental ballistic missile test into the Pacific Ocean, Seoul’s demands on Washington are likely to return. In this context, the Washington Declaration serves as a temporary salve to intra-alliance dilemmas.
Despite these difficulties, the Yoon and Biden administrations can take two steps to ensure that the Washington Declaration can have enduring value for the alliance and achieve its stated goals of buttressing deterrence of North Korea.
First, the Yoon administration should enthusiastically communicate to South Korean strategic elites that it believes in the sufficiency of existing extended deterrence practices, including the new mechanisms announced in the Washington Declaration. Yoon has said this publicly alongside Biden in Washington, but others will require convincing back in Seoul.
Second, while the Washington Declaration is a laudable software upgrade for the alliance, it does little to address the ongoing downward spiral in the alliance’s relations with North Korea. The declaration devotes just one sentence to diplomacy with Pyongyang. Although prospects continue to be dim for meaningful engagement, the United States and South Korea must recognize that assurances are complementary to credible deterrent threats against North Korea. Just as the alliance communicates the severe consequences that would follow nuclear use and other adverse military action by North Korea, so too must it assure Pyongyang that its restraint will be met with restraint in kind.
Third, while the United States, as a matter of alliance management, will be motivated to address Seoul’s anxieties about extended deterrence through nuclear reassurance, Washington should be cautious of rendering extended deterrence synonymous with nuclear extended deterrence. The Washington Declaration correctly notes that South Korea “is backed by the full range of U.S. capabilities, including nuclear.” While nuclear weapons have grown increasingly salient in Seoul’s domestic debates, the overwhelming majority of the alliance’s practical capabilities that will be relevant to deterring North Korean adverse action, including initial nuclear use, remain conventional.
