The situation on the Korean Peninsula is increasingly precarious. Amid a historic low in inter-Korean relations and the wider Indo-Pacific region’s rapidly deteriorating security environment, the risk of nuclear war is growing. Meanwhile, the United States (US) is simultaneously confronting an adversary with a growing appetite for risk and an ally with a growing appetite for assurance—particularly with US nuclear weapons.
American efforts to maintain stability on the peninsula thus far have required both the prevention of unmanageable aggression by The Democratic People’s Republic of Korea (North Korea or DPRK) and the maintenance of a cohesive alliance with the Republic of Korea (South Korea or ROK). As such, employing nuclear weapons in ways that both deter Pyongyang and assure Seoul has remained a strategic imperative for Washington for decades. However, the evolving conditions on the Korean Peninsula create new challenges for the US in simultaneously maintaining these two objectives, exposing limitations to the power of nuclear weapons to effectively meet them.
While the requirements for deterring North Korea and assuring South Korea are related, they are not entirely interchangeable and, in some cases, prove contradictory. Military solutions alone, particularly ones centered on nuclear weapons, continue to carry a serious risk of triggering a second, and presumably bloodier, Korean War. Thus, striking a balance between deterring North Korea and assuring South Korea amid evolving regional security conditions to limit the risk of nuclear war demands a creative reenvisioning of US policy in the region. This should begin with an exploration of policy options aimed at addressing the alliance’s current overreliance on nuclear weapons.
The Dual Threat
The US is currently confronting two simultaneous trends that are uprooting stability in Northeast Asia—a North Korea that is increasingly risk-acceptant and a South Korea that is demanding more US commitment, particularly with nuclear weapons. The notion of North Korea being more willing to accept risk than its counterparts is not new, with the state regularly taking escalatory measures in pursuit of short-term gains for decades. This bellicose behavior has continued into 2024, with the firing of artillery shells toward the disputed Northern Limit Line, the flight test of a solid-fuel intermediate-range missile armed with a hypersonic warhead, and the test of its nuclear-capable underwater attack drones, among ceaseless bellicose statements. What makes these recent developments particularly concerning, though, is the coinciding announcement by Kim Jong Un that the country will abandon an objective that has been integral to the DPRK’s inter-Korean policy for decades—peaceful reunification. This change is one of the most consequential changes in North Korean policy since its Cold War decision to pursue nuclear weapons.
In an early January address, Kim ordered the revision of the North’s constitution and propaganda guidelines to remove any references to “peaceful reunification,” “great national unity,” or to South Koreans as “fellow countrymen.” This change shortly proved to be more than just rhetorical, with Pyongyang quickly making institutional adjustments, such as closing its agencies dedicated to reunification, demolishing a symbolic reconciliation monument, and scrapping all agreements related to economic cooperation with South Korea. Kim’s changed attitude toward Seoul has introduced a new driver of insecurity and unpredictability on the peninsula, leaving many Korea watchers concerned about the future.
At the same time, the US-ROK alliance has undergone a serious crisis of confidence. Multiple factors, including North Korea’s advancing missile and nuclear capabilities and a significant degradation of trust within the alliance under the former US President Donald Trump’s term in office, have strained the relationship in recent years. Although much of the cohesion lost during Trump’s presidency appears to have been regained by former President Joe Biden’s efforts, Trump’s potential reelection remains a cause for unease for many in the region. As such, differences between how the two allies believe effective extended deterrence should look continue to grow.
The reality is the alliance is already more than capable of both denying Pyongyang any perceived benefits of aggression and responding to nuclear use. South Korea has upgraded its conventional capabilities in recent years—including a $4 billion investment in new weapons—and the US maintains a clear conventional advantage over the North. Yet, despite a notable overmatch against the North Korean challenge conventionally, South Korea has continued to grow more insistent that the US demonstrate its nuclear commitment as well. Seoul’s assurance anxieties became especially salient early last year, with the intensification of longstanding public discourse about the potential for South Korea’s own nuclearization culminating in the first public articulation of such a possibility by an ROK president.
This growing appetite for nuclear assurance led to the joint 2023 Washington Declaration, which significantly grew the nuclear dimension of the alliance. The Declaration established a new Nuclear Consultative Group, augmented tabletop exercises between the allies on nuclear weapons issues, and committed the US President to make every effort to consult with South Korea’s president before using a nuclear weapon on the peninsula—all notable upgrades to the bilateral alliance. Still, while the Washington Declaration may have turned down the volume on some South Korean hawks for now, it did not permanently snuff the lure of nuclear weapons in Seoul.
Addressing South Korea’s insecurities in meaningful ways is crucial to preserving stability on the peninsula and averting nuclear war, but assuring Seoul has been described as feeling “like pouring water into a bucket with a hole in the bottom.” So long as North Korea’s asymmetric capabilities continue to grow, it is unlikely that any alliance agreements or political declarations can ever fully ease South Korean anxieties and desires for protection under nuclear weapons. Especially in the face of impending stressors, such as the upcoming US election, serious doubts remain about whether the alliance’s assurance gap has been durably filled.
The Complex Relationship Between Extended Deterrence and Allied Assurance
Many of the actions pursued by the US in the region are designed to satisfy both objectives of deterring North Korea and assuring South Korea. Conducting regular joint military exercises, maintaining a “constant presence“ of strategic assets in the region, and reinforcing its commitment to the alliance through occasional political declarations all work together to demonstrate the US’ capability and will to both Koreas to protect its interests and allies in the region. Still, while several requirements of deterring North Korea and assuring South Korea are related, they are not all fungible and, in some cases, can be contradictory.
What the US believes will deter North Korea is not always what assures South Korea. The clearest illustration of this is Washington’s policy of strategic ambiguity. The US maintains that any use of nuclear weapons by the DPRK would result in the “end of its regime,” but what would this look like? Washington delineates no repercussive specifications—be it one hour or one week from the incident, be it against Kim Jong Un solely or any potential successors, be it unilaterally or with the help of its regional allies. Most importantly, from Seoul’s perspective, the US does not commit to a particular type of response to any North Korean use of nuclear weapons, be it conventional or nuclear.
The language of the US Nuclear Posture Review was carefully crafted in this way, allowing Washington flexibility in its response options while leaving its adversary in the dark, culminating in what the US believes is its strongest deterrence posture. However, because of the existing fears of abandonment that persist in South Korea, this ambiguous posture, in some cases, reinforces mistrust in the alliance. While the American perspective is that this ambiguity is solely in how it will respond, not if it will respond, South Korean officials have expressed concern that this ambiguity represents an overall lack of commitment from the US to respond, much less to respond with nuclear weapons.
Similarly, what assures South Korea is not necessarily what the US believes will deter North Korea. ROK officials and analysts alike have presented several proposals that they believe would alleviate South Korean anxieties, the most pervasive being a request that the United States commit to use a nuclear weapon in response to any use of nuclear weapons by North Korea. Some South Koreans hold a strong—almost moral—conviction about the need for such a “nuclear-for-nuclear“ force posture, reflecting a growing perspective in the country that only nuclear weapons deter nuclear weapons. This common perception has been a core motivation behind desires in the country for a South Korean bomb. Yet, the reluctance of US officials to concede to this demand hints at a fundamental difference in American and Korean beliefs about the operational value of nuclear weapons for deterring North Korea.
US doctrine has explicitly rejected a nuclear-for-nuclear approach, one official explaining, “There’s no automaticity in [the US’] approach, whether a nuclear use or non-nuclear use against the United States or our allies.” Washington instead chooses to abide by a variety of constraints on its nuclear considerations. Legally, the US has committed to apply the law of armed conflict to any use of its nuclear weapons. Operationally, US analysts have raised doubts about the reasonability of using nuclear weapons in such a geographically condensed area as the Korean Peninsula. As a result, Washington maintains a relatively conservative menu of options for nuclear use—much more conservative than many in Seoul would prefer. US officials believe committing to an automatic nuclear response of any kind, without considering the “context in which an attack occurred,” would detract from the credibility of US deterrence with North Korea.
Nuclear Weapons Are Not a Silver Bullet
Despite the ubiquitous fixation on nuclear weapons among alliance planners and analysts, making the alliance more nuclear is neither the solution to the persisting assurance gap nor the key to answering the North Korean threat. Increasing the salience of nuclear weapons, evidence suggests, is actually fueling the alliance’s assurance crisis. Expanding the alliance’s reliance upon nuclear weapons reiterates the idea that only nuclear weapons deter nuclear weapons, which, in turn, drives the pro-nuclear sentiment among the South Korean general public. As a result, the South Korean government can manipulate this public discourse to garner concessions from the US, both challenging Washington’s nonproliferation efforts and illuminating fractures in the alliance to be exploited by North Korea. An obsession with nuclear weapons—especially when it is to the neglect of the US and ROK’s more-than-sufficient conventional capabilities—is detrimental to the alliance.
Instead, the US should turn its attention to reducing the salience of nuclear weapons. This does not just boil down to limiting the alliance’s military dependence on nuclear weapons, although this is an important starting point. Reducing the salience of nuclear weapons also includes a multitude of efforts on various levels of engagement, such as improving the nuclear weapons information environment for South Korean officials and civilians alike, educating South Koreans on the grave environmental and humanitarian impacts of nuclear weapons, emphasizing the US commitment to international humanitarian law during alliance planning, and utilizing the NCG as a forum to address Seoul’s concerns of being left in the dark on nuclear issues.
The US should also immediately prioritize risk-reduction efforts with North Korea, aimed at disincentivizing nuclear first use by Pyongyang and averting unintended nuclear crises. This demands concerted reflection on the alliance policies that create such use-it-or-lose-it pressures in Pyongyang, such as Seoul’s risky strategy of preemption through Kill Chain and Washington’s exploration of options to disable North Korean missiles prior to their launch. This may also include efforts to warm relations with Pyongyang—such as engaging with North Korea on nontraditional security topics like climate change and eliminating barriers to ongoing scientific diplomacy endeavors. Although much political courage would be needed, the gains from prioritizing creative risk-reduction measures with North Korea over immediate disarmament far outnumber the costs.
These efforts need to reach beyond the alliance as well. It is difficult to convince an ally that nuclear weapons are not the answer to all its security woes, while global nuclear modernization and expansion efforts all feed into this narrative. As more countries begin to explore the prospect of going nuclear—even if in largely hypothetical terms for now—the US must begin to reckon with the growing incompatibility of nuclear fetishism and nonproliferation.
Nuclear weapons alone cannot solve the political issues of deterrence and assurance. Instead, reducing the preeminence of nuclear weapons as the foundation of the ROK-US alliance, combined with meaningful risk-reduction efforts and political engagement, may have a profound effect in both confronting the nuclear enthusiasts in South Korea and averting the risk of nuclear war with North Korea.
