A major priority of the Biden administration has been to reinforce the credibility of the U.S. extended nuclear deterrent to South Korea. Working closely with the administration of President Yoon Suk Yeol, it has made substantial progress, especially with the adoption of the Washington Declaration in April 2023.

These efforts, while still a work in progress, have strengthened deterrence of North Korea and, at least for the time being, may have curbed and perhaps reduced South Korea’s interest in acquiring its own nuclear deterrent..

But reassuring an ally that the United States will come to its defense, even at the risk of putting the American people in grave danger, is an inherently challenging and never-ending process.

Seoul and Washington will need to sustain their current momentum in implementing the Washington Declaration and fulfilling its potential.

And that will depend on maintaining a close, trustful, and mutually accommodating relationship between the two allies well into the future, even in the face of possible leadership changes in both capitals.



The principal reason for strengthening the U.S. extended nuclear deterrent has been the rapid quantitative and qualitative advancement of North Korea’s nuclear and missile capabilities, including solid-fueled intercontinental ballistic missiles (ICBMs) capable of reaching the American homeland and tactical nuclear weapon systems that Pyongyang threatens to use preemptively against South Korea in a crisis.

This relentless expansion and diversification of North Korea’s nuclear arsenal have been accompanied by continuing uncertainty in South Korea about the reliability of U.S. security guarantees, especially the U.S. nuclear umbrella.

Concerns in Seoul about the reliability of U.S. security guarantees are nothing new; they date back to the presidencies of Richard Nixon and Jimmy Carter.

Those concerns were renewed by President Trump’s dismissive attitude toward U.S. alliances and his threat to withdraw U.S. forces from the South if his exorbitant demands for financial compensation for stationing the troops were not met.

The combination of the alarming growth of the North Korean threat and continuing uncertainty about the U.S. nuclear umbrella has led many South Koreans to consider alternatives to their current security posture, including the redeployment of U.S. nuclear weapons in the South, the adoption of NATO-type nuclear sharing arrangements, and the ROK’s acquisition of an independent nuclear weapons capability.

None of these alternatives is supported by the Biden administration. Instead, it has focused on shoring up the U.S.-ROK alliance, strengthening the allies’ individual and collective defense capabilities, and reinforcing the U.S. extended nuclear deterrent.

The goal has been both to deter North Korea and reassure South Korea and, in so doing, reduce ROK incentives for acquiring its own nuclear deterrent.

In 2022, the Biden and Yoon administrations intensified engagement on extended deterrence issues, including by convening the existing bilateral Extended Deterrence Strategy and Consultation Group (EDSCG) for the first time in over four years.

The Yoon administration welcomed U.S. efforts to strengthen deterrence, including the many high-level statements of U.S. commitment, stepped up joint military exercises and training, and the increased frequency of U.S. rotational deployments of strategic assets to the region.

But the South Koreans continued to press for more – a more permanent and visible U.S. strategic presence in and around the Korean Peninsula, a more influential role in developing extended deterrence policies, greater insight into U.S. nuclear planning, and a greater voice on whether and when U.S. nuclear weapons would be used on the Peninsula.

The United States has traditionally been reluctant to make changes in the extended deterrence status quo. It has maintained that it already has an effective, survivable deterrent and that modifications could increase the deterrent’s vulnerability, costs, and other practical difficulties and could dilute the exclusive role of the United States, especially the American president, in planning nuclear operations and deciding on the use of U.S. nuclear weapons.

Nonetheless, given its heightened concern about the North Korean nuclear threat and its recognition that better integration of U.S. and ROK capabilities could enhance deterrence, the Biden administration was prepared to work intensively with South Korea to find practical ways of accommodating its ally’s interest in playing a more prominent role in the planning and execution of U.S. extended nuclear deterrence policies.





The result of this collaborative effort was the Washington Declaration, adopted in April 2023 during President Yoon’s state visit to the U.S. capital. The document contains many notable elements:

• The United States committed to “make every effort” to consult with the ROK on any possible use of nuclear weapons on the Korean Peninsula.

• A new, senior-level bilateral Nuclear Consultative Group (NCG) was created to promote what the Declaration called “deeper, cooperative decision-making on nuclear deterrence.”

• The allies agreed to expand table-top simulations to assist in planning their combined response to nuclear contingencies.

• The allies agreed to jointly plan and exercise for contingencies in which South Korea would provide conventional support for US nuclear operations – for example, suppressing North Korean air defenses.

• South Korea agreed to closely connect its new and improving conventional strategic capabilities with the the alliance’s combined force structure.

• The United States committed to further enhance the “regular visibility” of its strategic assets in and around the Korean Peninsula.

• The United States reaffirmed that any North Korean nuclear attack against the ROK would be met with a “swift, overwhelming, and decisive response,” which President Biden later said would result in the end of the North Korean regime.

• South Korea stated that it has full confidence in US extended deterrence commitments and reaffirmed its allegiance to the Nonproliferation Treaty (NPT).

Not surprisingly, the Yoon administration portrayed the Washington Declaration as a major accomplishment. President Yoon called it “an unprecedented expansion and strengthening of the extended deterrence strategy,” even claiming that it upgraded the U.S.-ROK alliance to “a new paradigm based on nuclear weapons.”

With a view to his domestic audience, he highlighted those elements that could be seen as opening the door to a greater ROK voice in alliance nuclear decision-making.

The Biden administration also praised the Washington Declaration but characterized its benefits in more modest terms. President Joe Biden called it “a prudent step to reinforce extended deterrence” that would result in “closer cooperation, closer coordination” between the allies.

At the post-summit press conference, while Yoon talked about the planning and execution of “joint operations,” Biden chose to point out that he has the sole authority to use U.S. nuclear weapons.

The reaction to the Washington Declaration by South Korean non-governmental experts, former officials, and editorial writers was generally positive. They gave credit to the Yoon administration for pushing hard for a greater ROK role in extended deterrence.

They also praised the Biden administration’s strong determination to invigorate the alliance and bolster deterrence of the North, including by declaring that any DPRK use of nuclear weapons would result in the end of the Pyongyang regime.

At the same time, knowledgeable experts pointed out that, in many areas, the Washington Declaration only restates or builds incrementally on previous alliance policies, practices, and mechanisms – and should hardly be regarded as a new paradigm for the alliance.

Some critics argued that, notwithstanding the declared intention for the ROK to play a more significant role, the asymmetry inherent in extending deterrence – with non-nuclear ROK dependent on security guarantees provided by its nuclear-armed U.S. protector – would remain and would prevent South Korea from doing what many critics considered necessary to ensure its security: acquiring its own nuclear deterrent.

The Chosun Ilbo was one of the most vocal critics. Its editorial on the Biden-Yoon summit – entitled “Nuclear Deal with U.S. Tightens Korea’s Shackles” – conceded that the Washington Declaration will give the ROK a better understanding of the U.S. nuclear umbrella and will give Seoul “some say” in the use of American nuclear weapons against North Korea.

But it argued that these gains came at too high a price. By agreeing to remain in the NPT, South Korea “relinquished any ambition to arm itself with nuclear weapons in the face of the North Korean threat.”

Even among supporters of the summit outcome, it was recognized that the Washington Declaration was only an initial step.

It established a promising framework for collaboration by the allies, but its value in reinforcing extended deterrence would depend on how closely and effectively the United States and South Korea were prepared to work together to implement that framework, turning its goals and principles into detailed, enduring policies and practices.



So far, after seven months implementing the Washington Declaration, the record is positive. Both sides have worked hard to maintain the momentum from the April summit. Progress has been made on several of the elements contained in the Declaration.

The tempo of bilateral engagement has been impressive. The newly established NCG held its inaugural meeting in July and will meet again on December 15. Other consultative mechanisms (including the EDSCG and the U.S.-Korea Integrated Defense Dialogue) continued their work.

In November, defense ministers spent much of their Security Consultative Meeting (SCM) following up on the Washington Declaration. Extended deterrence in a trilateral framework was a major topic when Biden met with his ROK and Japanese counterparts at Camp David in August and on the margins of the Asia-Pacific Economic Cooperation summit in November.

In addition to these senior-level contacts, U.S. and ROK officials held frequent working group meetings and video conferences to advance the Washington Declaration agenda.

The United States made good on its commitment to increase the frequency and visibility of its rotational deployments of U.S. strategic assets to the region, including with the first port visit of a ballistic missile-carrying submarine in 40 years; the first-ever landing of a B-52 bomber in South Korea; two visits of carrier battle groups; and a visit of a guided missile submarine (SSGN).

In response to a question at the SCM, Secretary of Defense Lloyd Austin said it was realistic to maintain the current tempo of U.S. strategic asset deployments.

In their post-April engagements, the allies have begun to put flesh on the bones of the Washington Declaration.

They have discussed joint planning for South Korea’s conventional support of U.S. nuclear operations; worked on security and information sharing protocols to facilitate exchanges of sensitive information; planned upcoming tabletop simulations to assist in developing a combined response to North Korea’s use of nuclear weapons; revised their Tailored Deterrence Strategy for the first time in ten years to reflect changes in the security environment; conducted the largest-ever combined joint live-fire exercise and planned further expansion of the scope and scale of joint exercises in 2024; examined technical means to enable secure, urgent leader-level communications in a nuclear crisis; and in general considered on how to better integrate ROK and U.S. conventional and nuclear deterrence and response capabilities.





Both sides seem satisfied with the start they have made. But they understand that they have far to go to realize the potential of the Washington Declaration. And they will need to overcome or at least narrow differing perspectives on some key issues.

One challenge is that Washington and Seoul don’t exactly see eye to eye on how to respond to a North Korean nuclear attack.

Arguing that only nuclear weapons can deter the use of nuclear weapons, the South Koreans have sought a commitment by the United States that it would respond with nuclear weapons if Pyongyang used nuclear weapons against the South.

While promising a “swift, overwhelming, and decisive response” that could well include nuclear weapons, Washington has been unwilling to commit to nuclear use in all circumstances. It has maintained that, in some circumstances, a conventional response would be effective and more suitable to the target and that a nuclear response would be unnecessarily escalatory.

In the course of detailed discussions on the effectiveness and implications of conventional and nuclear response options in various scenarios, the allies can hopefully reach a common understanding of this critical issue.

Another challenge is satisfying each side’s demand for more information about the other side’s plans and practices. South Koreans are calling for more information about, and a greater role in, US nuclear plans and operations.

For decades, the United States regarded nuclear deterrence on the Korean Peninsula as its exclusive responsibility and stiff-armed ROK requests for information about its nuclear policies and plans.

But given its recognition that deterring the current North Korean threat will require closer coordination between alliance conventional and nuclear capabilities, Washington now seems willing to grant its ally a more significant role – including in providing conventional support for U.S. nuclear operations – and to share more insights into U.S. nuclear planning and operations.

But where it will draw the line is not yet clear. Among the things that are clear is that the American President will retain sole authority to order the use of U.S. nuclear weapons (although the South Korean president will have the opportunity, like NATO leaders, to weigh in on that decision).

And Washington will resist developing a joint plan for nuclear operations akin to the joint operational plans (OPLANs) it has long developed with the ROK in the conventional domain.

For its part, Washington sees information-sharing and joint planning as a two-way street, and it has demands of its own.

It strongly supports the ROK’s development of robust conventional military capabilities. But it believes those capabilities – including the Kill Chain and Massive Punishment and Retaliation components of the ROK’s “three-axis” strategy – must be closely integrated with the alliance’s combined command structure to reduce the possibility of uncoordinated military actions that could precipitate a rapidly escalating conflict.

Part of the impetus for the ROK’s three-axis strategy was to demonstrate, both to North Korea and the South Korean public, that South Korea had its own formidable, independent capabilities and was not overly reliant on the United States.

It is not yet clear how receptive Seoul will be to coordination efforts that could be viewed as limiting its ability to operate autonomously.

Addressing each other’s requests for greater sharing of information and enhanced coordination of nuclear and strategic operations will be among the most sensitive issues the allies will need to tackle in the months and years ahead.



The Washington Declaration is a work in progress. At this early stage, it can hardly be considered transformational for the U.S.-ROK alliance.

But it has the potential to profoundly alter the alliance’s division of labor – to move it in the direction of a more tightly integrated, more mutually dependent, and more equal partnership, one that can more effectively counter the threat from the North.

Realizing that potential, however, will depend on strong leadership in Seoul and Washington. ROK leaders will need to be more active and assertive in making the case to South Korean opinion leaders and the public at large about the importance of the U.S. extended deterrent to ROK security, especially when compared to the risks and downsides of pursuing an independent nuclear weapons capability.

American leaders will need to overcome longstanding internal resistance to changes in the status quo that would give South Koreans a greater role in U.S. extended nuclear deterrence policies.

Fulfilling the promise of the Washington Declaration will also depend on maintaining the very close cooperation that has characterized the Yoon-Biden relationship and sustaining that cooperation in the face of future changes of administration in both capitals.

Already the political class in South Korea is heavily focused on the 2024 U.S. presidential election and the possible return of America First policies that could upend the gains for the alliance that have been achieved in the last few years.

To reduce the likelihood of reversals that could result from future government transitions, supporters of the alliance in Seoul and Washington are calling on the Yoon and Biden administrations to accelerate implementation of the Washington Declaration and to do whatever they can to institutionalize the progress that they make.

Even at this early stage of implementation, adoption of the Washington Declaration – together with high-profile visits of U.S. strategic assets and frequent meetings of U.S. and ROK leaders and other senior officials demonstrating alliance solidarity and resolve – seem to have given a boost to South Korean confidence in U.S. security guarantees. And if a poll conducted by the Korea Institute for National Unification in late April-early May is accurate, there has been a modest but significant drop in South Korean public support for an independent nuclear weapons capability.

But the North Korean nuclear threat continues to grow and there is little current prospect that negotiations will eliminate or even reduce that threat, especially now that China and Russia have become increasingly aligned with Pyongyang and increasingly unwilling to cooperate with the United States and its allies to rein in its nuclear and missile capabilities. In these circumstances, the demand for strengthening the U.S. extended nuclear deterrent – and for South Korea to play a significant role in the planning and execution of that deterrent – will also continue to grow.

The Washington Declaration provides the framework for meeting that demand. But it will require governments in Seoul and Washington to remain committed to implementing that framework, to devote the substantial energies and resources needed to sustain positive momentum, to find practical ways to accommodate each other’s concerns and interests, and above all to maintain strong support for the U.S.-ROK alliance relationship well into the future.

By Robert Einhorn, Brookings (Honorary Reporter of Maeil Business Newspaper)

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