Experts react: The US and South Korea strike a deal on nuclear weapons. What’s next for the alliance?

US President Joe Biden welcomed South Korean President Yoon Suk Yeol to the White House on Wednesday to commemorate seventy years of the US-South Korea alliance and the war that forged it—but this state visit is no backward-looking affair. While the top items on the agenda (nuclear weapons and microchips) were invented nearer to 1900 than today, the two leaders are navigating the political tensions around those technologies to find a common future. Below, Atlantic Council experts break down the two leaders’ Washington Declaration on nuclear weapons, how the leaders are addressing Seoul’s concerns over US industrial policy, and more.

This post will be updated as the Yoon visit unfolds and more reactions come in.

Click to jump to an expert reaction:

Markus Garlauskas: This is the day US-South Korea truly became a nuclear-armed alliance

Jieun Baek: Yoon puts digital freedom in North Korea on the agenda

Matthew Kroenig: A helpful step forward on nuclear deterrence—but also a stopgap measure

Robert M. Soofer: Missing from the package of assurance measures is US homeland missile defense

Rachel Whitlark: US assurances keep South Korea away from its own nuclear weapons—for now

Jessica Taylor: US elections and a transition of South Korean command raise bigger questions 

Fredrick “Skip” Vincenzo: More can be done to convince North Koreans not to follow Kim Jong Un into war

Thomas Cynkin: Trading Los Angeles for Seoul? The Washington Declaration and the US nuclear umbrella

Lauren D. Gilbert: Strengthening US-South Korea-Japan trilateral cooperation

Gittipong “Eddie” Paruchabutr: South Korea’s entertainment industry is also part of integrated deterrence

This is the day US-South Korea truly became a nuclear-armed alliance

The new Nuclear Consultative Group that Biden and Yoon announced today for the South Korea-US alliance is a major step forward for the alliance’s efforts to deter, prepare for, and respond to North Korea’s nuclear coercion tactics and aggression. Today may be marked as the day that the US-South Korea alliance truly became a nuclear-armed alliance—even if the nuclear weapons are still US-owned and US-controlled, we can now consider nuclear weapons to be an alliance capability.

However, this is just a step and one that requires a great deal of follow-through to realize its promise. This announcement opens the door for a whole new level of necessary hard work in the alliance on nuclear issues, as the presidents alluded to today. War plans and training will have to be continually revised to account for new approaches and new realities, particularly including North Korea’s rapidly growing strategic and tactical nuclear and missile capabilities. The alliance will have to conduct new military exercises and table-top simulations with nuclear considerations at the forefront, incorporating the lessons learned each time. Mindsets will also have to change—rather than focusing on how the United States will “provide” extended nuclear deterrence to South Korea through threats of US nuclear punishment, the focus going forward should be on how to integrate US and South Korean capabilities and approaches to a wide spectrum of nuclear and non-nuclear aggression. The mindset within the alliance will also have to fully come to grips with the harsh reality that nuclear deterrence may fail, meaning that the alliance should be prepared to be resilient in the face of nuclear attacks and to launch a coordinated counterattack as an alliance. 

Today’s important step may be moving onto uncertain new terrain for the US-South Korea alliance, but this is not new territory for the United States. In fact, it is a step that was probably long overdue. Experts in South Korea and the United States had been openly advocating for such a mechanism for years, often citing the model of NATO’s Nuclear Planning Group (NPG), which was founded in 1966. There is a reason that NATO is held up as an example of how nuclear and non-nuclear armed allies can work together on nuclear deterrence and response. Even if NATO’s nuclear mechanisms are not perfect and the US-South Korea alliance is different from NATO in many ways, there is much to be learned from over seventy years of working with non-nuclear US allies in the nuclear-armed NATO alliance. Washington should also work with NATO allies to help ensure that South Korea will be invited to learn from NATO more directly, through involvement in NATO deterrence-related institutions and exercises. This should include, for example, official observer status for these allies in NATO’s Steadfast Noon nuclear exercises, invitations to selected NATO NPG activities, and regular participation in NATO nuclear educational programs. 

Markus Garlauskas is director of the Scowcroft Center for Strategy and Security’s Indo-Pacific Security Initiative and former US national intelligence officer for North Korea.

Yoon puts digital freedom in North Korea on the agenda

Yoon’s public recognition of North Korea’s grave abuses of its citizens, and his prioritization of “promoting the freedom to use digital technology and services as one of the universal values of mankind” is an understated highlight from last week’s US visit that warrants more attention from the United States and its allies. Extending this freedom to North Korean people must be a priority for the US-South Korea alliance to achieve its long-term policy goals in North Korea.

While the Washington Declaration did not mention human rights, Yoon used his speech to the US Congress to discuss North Korea’s indisputable human-rights abuses and plead with the international community to raise awareness of and improve the human rights situation in North Korea. 

In his speech on “the challenges of freedom” at Harvard Kennedy School on April 28, Yoon spoke at length about how the totalitarian nature of North Korea undermines freedom and democracy for the Korean peninsula and the international community. Furthermore, he said, “The digital order… must maximize the freedom and welfare, guarantee free opportunities, and most of all, provide consideration for the marginalized and vulnerable populations… The Republic of Korea will throw its full weight behind building a fair digital order that is grounded in universal justice.” 

The North Korea problem is unique in that the solution to its nuclear problem and human-rights crisis is the same, which is to compel the regime to fundamentally change its relationship with its people. Extending the freedom to use digital technologies and services to North Koreans is one of the best tools to create the conditions to induce North Korea to better respect the rights of its people, increasing the prospects that Pyongyang will eventually accept denuclearization. Such efforts must be intertwined with every aspect of the United States’ and South Korea’s policy priorities in North Korea, because if the current regime were to fundamentally change certain core values, this changed environment would encourage the regime to pursue a less hostile relationship with the outside world and deescalate its nuclear program.

Jieun Baek is a non-resident senior fellow at the Scowcroft Center’s Indo-Pacific Security Initiative. She is also the research manager for technology and human rights in North Korea at Harvard Kennedy School’s Carr Center for Human Rights Policy.

A helpful step forward on nuclear deterrence—but also a stopgap measure

Assuring allies is a stated goal of US nuclear strategy. By assuring allies that they are protected by US nuclear weapons, the United States can maintain stability in important regions and dissuade our allies from building independent nuclear arsenals, contributing to our nonproliferation goals.

Presently, the greatest challenge to assurance is South Korea. In the face of a growing North Korean threat, a majority of the South Korean public now supports building an independent nuclear arsenal.

During the Cold War, the United States assured South Korea in part by maintaining forward-deployed nuclear weapons on Korean territory. They were removed at the end of the Cold War, and some argue that they should be returned. 

The Biden administration’s announcement aims to take measures short of nuclear deployments to assure South Korea. The administration renamed and promised to deepen long-standing dialogues between Washington and Seoul on nuclear issues.

This is a helpful step forward. There is more the United States can do to strengthen assurance short of deployments, such as more detailed discussions on nuclear deterrence scenarios. This announcement also gives a concrete win to Yoon to bring home to Seoul.

Ultimately, however, this is a stopgap measure. To deal with the growing North Korean and Chinese nuclear threats, the United States will soon need theater nuclear weapons deployable and deployed to Asia.

One obvious option is the nuclear-armed sea-launched cruise missile (SLCM-N). This system was put in place by then US President Donald Trump and canceled by Biden. But bipartisan majorities in Congress have restored funding to the program.

Matthew Kroenig is vice president and senior director of the Atlantic Council’s Scowcroft Center for Strategy and Security and the Council’s director of studies. He formerly served as a nuclear-weapons expert in the US Department of Defense and intelligence community.

Missing from the package of assurance measures is US homeland missile defense

The set of measures announced by Biden and Yoon will be helpful in reassuring a nervous South Korean population that the United States can be counted upon to help deter North Korean nuclear threats. The regular, temporary deployment of US nuclear-capable forces to South Korea, creation of a new bilateral nuclear consultative group, and better integrating South Korean conventional assets into the nuclear deterrence mission should help reinforce the deterrence signal meant for the North Korean leadership.

Yet these important steps may not address fully the underlying dilemma that provokes South Korean angst over the US nuclear umbrella: Would the United States use its nuclear weapons against a North Korea that is growing its capability to target American cities with nuclear weapons? Having the nuclear capabilities to strike North Korea is only part of the deterrence equation. The United States must also convince the adversary that it has the will to use these weapons in the face of nuclear retaliation. 

The United States today minimizes that risk through the deployment of a national missile defense system comprised of forty-four long-range ground-based interceptors. The Biden administration will update the system and expand the number of interceptors by twenty starting in 2028, though it is unclear whether this will be sufficient to stay ahead of the North Korean intercontinental ballistic missile (ICBM) threat.

The United States does not rely only on missile defense to counter the North Korean threat. Rather, it employs missile-defeat tactics meant to eliminate the missile threat prior to launch. Through this combination of missile defense/defeat and the threat of nuclear retaliation, the United States signals to North Korea that any nuclear use against the United States or its allies would be both futile and fatal. By taking steps to protect the homeland against North Korean ICBMs the United States makes clear its willingness to run risks on behalf of its allies. In this sense, homeland missile defense should be included in the package of assurance measures discussed by the two countries.

Robert M. Soofer is a senior fellow in the Forward Defense practice of the Atlantic Council’s Scowcroft Center for Strategy and Security, where he leads its Nuclear Strategy Project. He formerly served as US deputy assistant secretary of defense for nuclear and missile defense policy.

US assurances keep South Korea away from its own nuclear weapons—for now

News from the White House today reveals that the United States will, for the first time, provide South Korea with a central planning role for the use of US nuclear weapons in conflict scenarios with North Korea. It is a move akin to how the United States integrates NATO allies in conflict preparations and plans. While perhaps challenging for the larger nuclear non-proliferation regime and significant for security dynamics and stability on the Korean Peninsula, recent events make this increased nuclear sharing understandable. This growing and deepening cooperation in the nuclear realm is one way the United States is attempting to reassure South Korea about its commitment to protect and defend its ally amid a worsening security environment. Similar are the Freedom Shield and Warrior Shield FTX military exercises the two states jointly conducted last month—the largest such exercises undertaken in five years. 

Such reassurance is needed in light of former US President Donald Trump’s public discussion of withdrawing US troops from South Korea unless it upped its financial contributions for hosting them (and the possibility of a second Trump administration or election of a Trump acolyte in 2024 who makes good on such ideas). Further integration of the South Koreans into US planning can also be understood as a way to try to stave off growing domestic interest in an indigenous South Korean nuclear weapons option, which may be an increasingly popular conversation topic ahead of South Korea’s presidential elections in 2027. Moreover, an expanding North Korean nuclear arsenal understandably generates increasing nervousness and insecurity among South Koreans. These ongoing dynamics between the United States and South Korea are emblematic of the kinds of difficult conversations and tradeoffs Washington may need to make with its currently non-nuclear allies in a worsening regional security environment. 

Currently, the United States remains committed to upholding nuclear non-proliferation norms, including taking increasingly significant steps to try to forestall allied proliferation. However, given that tensions are growing in key regions around the globe and the decision to attempt to acquire nuclear weapons is ultimately a state’s own choice, the United States may soon need to ask uncomfortable questions and reexamine its historical commitment to keeping allies away from their own nuclear weapons. A point may arrive where allied reassurance hits its limit and/or the United States views allied proliferation as augmenting the US security position vis-à-vis some hostile actor or actors rather than undermining it. US policymakers would do well to think through these difficult tradeoffs sooner rather than later.

Rachel Whitlark is a nonresident senior fellow in the Forward Defense practice of the Atlantic Council’s Scowcroft Center for Strategy and Security.

US elections and a transition of South Korean command raise bigger questions 

The Washington Declaration demonstrates an important step toward strengthening the US-South Korea alliance. However, in short order it may not have the ability to decrease the South Korean public’s desire for an indigenous nuclear weapon capability. The declaration and plans for rotation of a US nuclear-armed submarine to South Korea is likely to draw ire from not just North Korea but China as well. However, overall nuclear employment decision-making will still rest with Washington.

Any concerns surrounding US abandonment will likely not be resolved within one US administration. With the 2024 US presidential election looming, it is unclear whether the winner of the election will hold similar views toward cooperative decision-making on nuclear deterrence.

Yoon’s declaration of commitment to the Nuclear Non-Proliferation Treaty is a quick turn from his earlier comments in which he signaled possible support for South Korea one day developing its own nuclear weapons. It begs the question of whether Washington’s decision to further include South Korea in this manner after Yoon’s comments will extend to other regional allies. And in the long term, the declaration does not address concerns surrounding the transition of wartime operational control of the allies’ joint forces to South Korea. The question remains: How can a South Korean general be in charge of the South Korea-US Combined Forces Command in a conflict when final say on nuclear weapons will always reside in Washington?

Jessica Taylor is a nonresident fellow in the Indo-Pacific Security Initiative at the Atlantic Council’s Scowcroft Center for Strategy and Security. She served in South Korea from 2019 to 2021 as an international relations strategist for the headquarters command staffs of United Nations Command, ROK/US Combined Forces Command, and US Forces Korea.

More can be done to convince North Koreans not to follow Kim Jong Un into war

The joint statement issued by Biden and Yoon comprehensively affirms the strength of the US-South Korea alliance and demonstrates the shared values of both nations. While it gives particular attention to North Korea’s rapidly advancing nuclear and missile programs, its sincerity of commitment across a range of issues provides a firm basis for further maturation of the alliance.

And yet, what the statement did not say also matters. North Korea is perilously close to being able to hold American cities at risk. Two weeks ago, it successfully tested what appears to be a solid-fuel long-range missile. Simply putting North Korea on notice that, as the leaders’ joint statement emphasized, “a DPRK nuclear test would be met with a strong and resolute response” might not be enough. Should North Korean leader Kim Jong Un have the audacity to test a long-range missile that successfully detonates a warhead, it’s likely because he believes that showing he possesses such a credible threat will make the United States too risk adverse to use meaningful force against him.

The danger is not that Kim might simply decide to attack South Korean or US cities but rather that this credible of a threat might give him potentially game-changing leverage because it would undermine the credibility of US deterrence. If Kim comes to believe he can deter a regime-ending response, he might decide he can “safely” use that leverage to coerce South Korea into favorable political concessions—something likely to result in miscalculation and conflict. This is a dangerous development that is decades in the making. Yoon and Biden inherited this mess and are not to blame for where we are, but it is time to start doing more than threatening consequences.

What can be done? Rather than focusing on deterring Kim—who may not be deterrable—the alliance should be aggressively waging a public information campaign to convince elites and others in North Korea that following Kim into conflict is the greater risk. If, at the brink of a conflict, they believe Kim is to blame, many of these ordinarily loyal people—in charge of critical weapons and military formations—might be deterred from engaging in hostilities if they feel they have credible alternatives for them and their families. Although not likely to be as successful as the peaceful capitulation of East German and Soviet elites at the end of the Cold War, if a critical mass come to believe that there is hope for them in a life after Kim, the potentially devastating costs of a war on the Korean Peninsula could be significantly reduced. A good start for the next joint statement might be to publicly commit to fair treatment for North Koreans if—should war occur—they refrain from fighting. 

Fredrick “Skip” Vincenzo, US Navy (ret.), is a senior fellow in the Indo-Pacific Security Initiative at the Atlantic Council’s Scowcroft Center for Strategy and Security.

Trading Los Angeles for Seoul? The Washington Declaration and the US nuclear umbrella

Throughout the Cold War and beyond, the United States has striven to ensure the credibility of its nuclear umbrella both to deter potential aggressors from attacking US allies by conventional or nuclear means and to reassure US allies that they do not need to deploy their own nuclear weapons. That credibility was strongest in cases where a potential adversary lacked the means of directly attacking the US homeland. With its own territory and people out of harm’s way, the United States would be able to retaliate with impunity. However, with the advent of nuclear weapons systems capable of directly targeting the United States, Washington and its NATO allies devised what would be described as a “seamless web of deterrence,” namely by ensuring dominance at each escalatory step. Thus, when the then-Soviet Union deployed intermediate-range ballistic missiles in Europe, the Carter administration with NATO concurrence responded by deploying its own. Were the Soviet Union to attack European NATO allies with intermediate-range nuclear weapons, the United States would be able to respond proportionately without having to resort to escalating and utilizing its central strategic nuclear forces.

The United States decided to withdraw its tactical nuclear forces from the Korean Peninsula in 1991, partly based on the hope that this would help persuade North Korea to forswear its nuclear weapons program. Since then, Washington has relied on periodic consultations in various formats to reassure its Korean allies that they can continue to depend on the US nuclear umbrella. However, with the advent of an aggressive nuclear modernization program by North Korea, which includes development not only of tactical nuclear weapons, but of ICBMs capable of striking the United States as well, the US nuclear umbrella covering South Korea appears to be fraying. Accordingly, the tide of South Korean public opinion has turned: seven-in-ten South Koreans now support developing their own nuclear arsenal, and a majority supports the return of US nuclear weapons to South Korea—long anathema to the South Korean public. This no doubt also reflects, in part, concerns about China. More broadly, China’s own nuclear buildup, its increasing backing of North Korea, and the growing risk of US-China military conflict over Taiwan all impinge on South Korea’s security.

Enhanced coordination of nuclear planning between Washington and Seoul as outlined in the Washington Declaration is designed to bolster Seoul’s confidence in the US nuclear umbrella. This is an important step forward and, in the short term, may alleviate pressure on South Korea to go nuclear. Ultimately, however, US force posture with respect to North Korea and a consistent, highly visible US commitment to the defense of South Korea will be the major determinants of whether this position remains sustainable.

Thomas Cynkin is a nonresident senior fellow in the Indo-Pacific Security Initiative at the Atlantic Council’s Scowcroft Center for Strategy and Security and the practice lead, Japan and Northeast Asia, of the Transnational Strategy Group, a global consulting firm operating at the nexus of policy and business.

Strengthening US-South Korea-Japan trilateral cooperation

The nuclear aspects that came out of the first state visit from a Korean president to the United States in twelve years were undoubtedly an important step for the alliance and a larger assurance of the United States’ extended deterrence. However, it was not the only theme of note. The leaders’ joint statement showed the Yoon administration’s commitment to working with the United States in building regional partnership and defending a “free and open” Indo-Pacific. In particular, the statement’s references to US-South Korea-Japan cooperation and maintaining peace in the Taiwan Strait show the two presidents’ dedication “to ensure the future of the Indo-Pacific is free, is open, prosperous, and secure.” 

After a significant deterioration in US-South Korea-Japan relations in recent years, President Yoon has dedicated himself to improving ties with Japan and developing trilateral cooperation with the United States and Japan—even directly stating that both presidents “agreed to continue our efforts in strengthening…trilateral cooperation.” This intention to improve both economic and regional defense measures among the three countries, alongside the statements on the UN Convention on the Law of the Sea, implicitly affirms the two countries’ commitment to defending against both a North Korean and a Chinese threat—either in separate contingencies or through a potential simultaneous conflict.

Yoon’s White House visit comes as public opinion is shifting in Korea. For the first time in recent history, Koreans consider China to be less favorable than Japan. It is crucial that the three democracies work together to build on recent progress. As relations continue to improve, the countries should work toward a formal institutionalization of trilateral security and economic mechanisms to enhance interoperability and cement increased cooperation, bolstering regional security and prosperity.

Lauren D. Gilbert is an associate director with the Atlantic Council’s Indo-Pacific Security Initiative (IPSI) within the Scowcroft Center for Strategy and Security.

South Korea’s entertainment industry is also part of integrated deterrence

Yoon’s historic visit to the United States commemorated seventy years of the US-South Korea security alliance. This alliance, so far, has successfully deterred a North Korean military invasion and provided a secure foundation for South Korea’s unparalleled accomplishments in economic growth, democracy, and culture.

Although the purpose of Yoon’s visit was rightly focused on nuclear deterrence amid a recalcitrant and increasingly capable North Korean nuclear threat, other accomplishments during the week advanced key aspects of integrated deterrence.

Before the formal US-South Korea summit, Netflix co-CEO Ted Sarandos met with Yoon at Blair House to announce a $2.5 billion dollar investment in South Korea over the next four years. As stated in Netflix’s announcement, South Korean stories are now “at the heart of the global zeitgeist.”  

Compelling stories created by the South Korean entertainment industry—from traditional values highlighted in Korea No. 1 to modern hits such as Squid Game and Crash Landing on You—resonate not only with general audiences seeking entertainment but also have a profound effect on North Korean society. 

South Korean narratives, when consumed by multiple segments of North Korean society, directly challenge Kim Jong Un’s manufactured justifications for his regimes near complete control over North Korean society and its aggressive actions against South Korea’s sovereignty. 

Efforts such as the Netflix deal advance South Korean programs, increasing the volume of narratives that can potentially find an audience inside North Korea. This alternative to state-controlled media in North Korea can directly support the US Department of Defense concept of integrated deterrence. National security leaders must account for and plan to support private and public initiatives with diplomatic, military, economic, and informational tools of national power.

During his address to Congress, Yoon showed he already understands the inherent potential of information power by stating “BTS beat me to the White House.” The South Korean band’s music and other key elements of South Korean culture are undoubtedly already in Pyongyang also.

Gittipong “Eddie” Paruchabutr is a nonresident senior fellow in the Indo-Pacific Security Initiative at the Atlantic Council’s Scowcroft Center for Strategy and Security. He recently retired after twenty-five years as a Psychological Operations (PSYOP) Colonel from the US Army.

Further reading

Related Experts: Matthew Kroenig, Robert Soofer, Rachel Whitlark, Markus Garlauskas, Jessica Taylor, Jieun Baek, Fredrick “Skip” Vincenzo, Thomas Cynkin, and Lauren D. Gilbert

Image: US President Joe Biden and South Korean President Yoon Suk Yeol hold a joint press conference after their meeting at the White House in Washington on April 26, 2023.