Deterring a Nuclear North Korea: What Does the Theory Tell Us?

Executive Summary

Deterrence has long been the centerpiece of security strategy on the Korean Peninsula. Over the past two decades, however, the security situation has undergone a fundamental change—deterrence now must account for a Democratic People’s Republic of Korea (DPRK or North Korea) armed with nuclear weapons and the ballistic missiles capable of delivering them.

These developments have raised questions about whether deterrence will remain effective on the Korean Peninsula and, by extension, whether deterrence theory is still relevant as a guide to policy generally. Indeed, many analysts have raised important concerns about deterrence and nuclear dynamics, observing that North Korea’s nuclear weapons may weaken US extended deterrence commitments, erode conventional deterrence on the peninsula, blur the lines between nuclear and conventional war, and increase the likelihood of large-scale North Korean military aggression.

While these concerns and others are crucial considerations, we argue that deterrence theory remains useful in addressing these challenges and responding to the changing security dynamics on the Korean Peninsula. We also assert that deterrence against North Korea is stronger than some fear.

In this report, we reassess deterrence dynamics on the Korean Peninsula by drawing on deterrence and international relations theory to identify the core components of effective deterrence—clear demands, credible threats and credible assurances—that are essential for deterrence success, with all established from the perspective of the deterrence target. We then assess the state of each of these components on the Korean Peninsula today.

Despite significant changes to security dynamics on the Korean Peninsula, we believe deterrence theory remains a helpful guide for policy. Furthermore, it is our assessment that while the ROK-US defense posture needs regular review and adjustments, strategic deterrence is not as fragile as many observers have argued. Instead, the more serious challenge will come from the possibilities of lower-level North Korean aggression and the accompanying dangers of miscalculation, accident, and inadvertent escalation that also require reassuring the Republic of Korea (ROK or South Korea) of the US defense commitment and strengthening the alliance.

Core Elements of Deterrence: Clear Demands, Credible Threats and Credible Assurances

Successful deterrence requires three elements, all of which must be established from the perspective of the deterrence target. Each of these elements can be difficult to achieve, and actions that are taken to strengthen credible threats may undermine credible assurances to the adversary. Moreover, different actors may misperceive the same signals, which can also potentially undercut deterrence. Here, we review each of the three elements, drawing on the literature to identify the requirements for effective deterrence on the Korean Peninsula.

Requirements for Successful Deterrence

First, deterrence requires a clear demand about what action the target should not take. This demand must be mutually intelligible for both the deterrer and the target, and the demand must be something the target can plausibly fulfill. North Korea poses numerous security challenges that the ROK-US alliance seeks to deter. The primary demand is clear: deterring North Korea from engaging in large-scale conventional aggression or nuclear use. Yet the process of setting deterrence goals has at times been hampered by the tendency to lump together a wide array of North Korean actions under the unanalytic heading of “provocations.” It may not be possible to deter all behaviors, and some provocations may be undeterrable at a reasonable cost. In the end, a clear conception of what can and should be deterred is essential. Chief among these should be deterring and deescalating to avoid the costliest outcome—a large-scale conflict in Korea.

Second, deterrence requires credible threats, such that if the target does not refrain from the objectionable act, it will either fail in achieving its goal or pay significant costs after crossing the line. Credible threats depend on clearly demonstrating the capability and resolve to fulfill the threat if the target does not comply. Regarding capability, North Korea would be faced with overcoming a high level of military power, including a modern and capable ROK military, the ROK-US alliance, a revitalized United Nations Command (UNC), and the US nuclear umbrella should it seek to challenge the alliance. If North Korea were to attempt to take on this array of military strength, the likelihood of any conflict going badly in short order is high, making it equally likely that Pyongyang would need to escalate to nuclear use, an action that would almost certainly lead to the end of the Kim regime. Thus, the odds of success are very low, given the military power North Korea would face. Importantly, Kim Jong Un is likely well aware of this outcome.

Concerning resolve, North Korean hopes of military success against ROK-US capability might be premised, in large part, on the use of nuclear threats to discourage US assistance, resulting in a quick victory over the South. DPRK leaders may believe that decoupling the alliance is possible through nuclear threats and assess that if taking on South Korea alone, it could succeed. Yet, this judgment relies on confidence that the Korean People’s Army would be able to go on the offensive and sustain operations that would lead to victory over a modern and capable ROK military that would certainly rise to defend the country. When viewing the full picture of the credibility of ROK-US deterrence, North Korea would face significant obstacles if it chose to challenge the alliance. The risks would be high and the consequences grim for North Korea if it embarked on this path.

Third, deterrence requires credible assurances to the adversary. As Thomas Schelling, one of the architects of modern deterrence theory, observed: “To say, ‘One more step and I shoot,’ can be a deterrent threat only if accompanied by the implicit assurance, ‘And if you stop I won’t.’”[1] Threats must be conditional on the target’s good behavior so that the promised punishment will not result regardless of its actions. Otherwise, the target is not offered a true choice and may believe it has nothing to gain from acceding to the deterrent demand. Both scholarly and policy discussions of deterrence have systematically discounted the importance of assurances to the target state. However, credible assurances are just as necessary for deterrence as clear demands and credible threats. Providing credible assurances in Korea has proven particularly difficult. North Korea and the ROK-US alliance are simultaneously seeking to deter each other, and both sides have little confidence in their adversary’s assurances to refrain from striking, even if they behave. Senior officials on both sides have noted the challenges of establishing credible assurances or “trust” on the peninsula.

Finally, for all three elements, effective deterrence requires that they are established from the target’s perspective. It does not matter whether the deterrer believes their demands are clear and their threats and assurances credible; it only matters if the target believes them. Thus, deterrence theory reminds us that the only judgment that matters is North Korea’s assessment of credible deterrence.

Deterrence Dilemmas

Tensions Between Deterrence and Reassurance

The US defense commitment to South Korea is an example of extended deterrence, where a security guarantee seeks to deter aggression against an ally. Extended deterrence rather than deterring an attack on oneself is always more challenging. While professing support for an ally is easy during peacetime, deterrence in a crisis becomes far more difficult when the risks and costs are more tangible and immediate, particularly if the adversary is armed with nuclear weapons. Over the past few years, the United States has undertaken numerous measures to reassure South Korea of its commitment to ROK security, including increasing the size and scale of military exercises and the periodic deployment of strategic assets to the peninsula, largely intended to reassure the South rather than deter the North. Washington and Seoul have also held several high-level meetings that ended with agreements to demonstrate the “ironclad” nature of the alliance through increased economic and technological cooperation along with deeper security planning, such as the Washington Declaration and the formation of the Nuclear Consultative Group that upgraded, packaged, and promoted existing mechanisms for improving defense cooperation, especially concerning nuclear deterrence.

But while efforts to reassure the ally and deter the target are linked, they may be distinct and sometimes in conflict. The target of deterrence, the adversary, is different than the “target” for reassurance. The motives, perceptions, and assessments of their security situation may be vastly different, particularly if the power relationships among the players have significant asymmetries. Actions taken to reassure an ally may have little impact on an adversary who is already sufficiently deterred. Excessive measures to reassure may inadvertently increase the adversary’s insecurity and threat perceptions in ways that prompt it to further increase its military capability, which can make crises less stable and escalation more likely. Moreover, given South Korea’s security worries, there will likely be continuing fears that “it’s not enough” regarding US gestures of resolve, prompting Seoul to further increase its own conventional capabilities that further fuel an arms race and undercut stability.

Though both sides may share a common goal in avoiding large-scale conventional conflict, there may still be security dilemma dynamics at play based on mutually reinforcing perceptions of threat. North Korean reactions to ROK-US military exercises indicate a significant insecurity on the part of Pyongyang, even though those exercises are aimed at shoring up the alliance’s defense capabilities. Conversely, South Korea’s poor strategic geography makes it particularly vulnerable to the prospects of North Korean aggression and makes South Korea more likely to view DPRK provocations as deeply threatening.

Managing Risk and Escalation

A second dilemma for a successful deterrence strategy is managing the challenges of risk and escalation. Following through on the threats to retaliate if deterrence fails carries risk; though the target has already disrupted the peace, the defender’s response to a deterrence failure raises the possibility of continuing the conflict or escalating to higher levels of violence, with both posing the likelihood of significant costs. Credible deterrence requires the target to be convinced of the certainty of the defender’s response; yet to follow through means the costs could increase dramatically, particularly if nuclear weapons are part of the calculus. Deterrence threats and the responses should deterrence fail must consider whether the retaliation should be proportional to the act or escalate with the intent to raise the costs further to lay down a marker for future deterrence.

For South Korea, any threat to respond occurs with the risk of starting a broader conflict, which would be particularly costly given the proximity of Seoul to the North Korean border. Should a clash escalate, North Korea could quickly launch rockets and long-range artillery rounds with devastating effect. Over the years, and despite Seoul’s vulnerability, South Korea has often been more willing to respond to North Korean actions with direct strikes on the DPRK, while Washington has been reluctant for fear of sparking a wider war. The most likely path to large-scale conflict on the peninsula today is not the failure of strategic deterrence in the face of deliberate North Korean aggression but, rather, the escalation of a crisis. While deterrence against a large-scale conventional or nuclear conflict appears strong, it may prove more challenging to deter lower-level aggression. Escalation risks are more pronounced given the profound strategic distrust and poor communication that pervade relations on the peninsula. The maturation of North Korea’s nuclear weapons capabilities might further embolden low-level aggression if North Korean leaders believe that nuclear weapons can provide a shield against significant retaliation.

In Korea, the advent and continued growth of North Korea’s nuclear weapon and missile capabilities have dramatically altered the security dynamics and raised serious concerns for stability and the outcome should deterrence fail. Successful deterrence remains central to ensuring peace and stability on the peninsula, and important adjustments have been made to bolster deterrence while enhancing reassurance. Yet, strategic deterrence is not as fragile as some suggest, and more attention needs to be devoted to risk reduction and decreasing tensions, along with addressing concerns regarding miscalculation, accidents and inadvertent escalation. In addition, more thinking must be done to address lower-level security concerns, particularly in the gray zone involving conventional forces and deterrence by denial considerations.


  1. [1]

    Thomas C. Schelling, Arms and Influence (New Haven, CT: Yale University Press, 1966), 74.


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