Renewing US Extended Deterrence Commitments Against North Korea

As COVID-19 upends millions of lives as well as traditional notions of security and the global economy, North Korea offers a stark reminder that the United States and its allies must still tend to military threats.[1] Pyongyang set a single-month record of nine missile launches this spring and declared it is now “more zealous for our important planned projects aimed to repay the U.S. with actual horror and unrest for the sufferings it has inflicted upon our people.” This was undoubtedly a reminder of Kim Jong Un’s New Year’s promise to soon unveil a “new strategic weapon” and his willingness to use it.

Does this portend a return to provocations and hostility reminiscent of 2017? There are good reasons to be concerned. Kim has called for “shocking” and “offensive” measures in charting a “new path” with the United States and South Korea. The return to missile tests, exercises and vitriol could be just the beginning. Similarly concerning are reports of political, economic and COVID-related uncertainty inside North Korea, given its purported history of lashing out in tough times to bolster domestic support for the Kim regime.

Understandably, extended deterrence issues have not received priority attention since denuclearization talks began in 2018. As prospects for those talks now appear grim, US and allied leaders may soon face decisions about how to revitalize a deterrence posture that has been largely dormant for two years. If and when they do, they will confront new challenges and old ones that have arguably worsened over time. Below, I take stock of those challenges and explore options for strengthening deterrence for a new era.

The Threat Grows On

(Source: Rodong Sinmun)

Kim was cryptic about what the “new strategic weapon” might be in his New Year’s address. But it is widely believed North Korea is working on a solid-fueled, mobile intercontinental ballistic missile (ICBM) that can deliver thermonuclear warheads anywhere on the globe. The Commander of US Northern Command hinted at such concerns when he recently testified before Congress. North Korea, he said, “may be prepared to flight test an even more capable ICBM design that could enhance Kim’s ability to threaten our homeland during a crisis or conflict.”

Indeed, a newly published United Nations report finds North Korea has not halted its nuclear or ballistic missile programs. Some estimates suggest it could now have enough fissile material to build over 50 weapons. And, while North Korea watchers look for signs of an upgraded ICBM, it has tested new types of regional missiles that can strike targets in South Korea and Japan with increasing accuracy and reliability as well as a new submarine-launched ballistic missile (SLBM).

Previous threats and exercises involving preemptive nuclear strikes on ports and airfields in neighboring countries suggest these new capabilities may be for purposes beyond retaliation. All signs point to an emerging strategy to enable limited nuclear first strikes against regional targets, while using a “new strategic weapon” to prevent full US retaliation by holding US cities at risk. Such a strategy aligns with many statements from North Korea’s leaders suggesting they may believe nuclear weapons can be used to compel adversaries, not just deter them, and even help unify the peninsula one day, by force, if necessary.[2] It is difficult to imagine the Kim regime ever concluding that it could actually launch a nuclear attack and survive, but the types of weapons Pyongyang is building, the way it exercises and its public pronouncements about using them make it hard to dismiss that possibility out of hand.

Extended Deterrence: Four Questions of Credibility

These developments put into sharp relief several questions about US extended deterrence. First, does North Korea believe the United States is willing to run nuclear risks to protect an ally (e.g., trade Seattle to save Seoul)? Signaling political resolve to take on such risk is no easy task, and presumably is becoming more difficult and costly for the United States. Perceptions of US resolve may have been damaged in recent years due in part to US President Donald Trump’s treatment of alliances as transactional arrangements rather than manifestations of core US national interests worth fighting to defend. This is especially poignant in South Korea’s case, given multiple reports that President Trump has questioned the value of the alliance and US forces stationed there.

Second, how does North Korea’s growing threat to Japan impact perceptions of US commitments to South Korea? More than once, North Korea has made clear that Japan is first on its nuclear target list. Leaders in North Korea might believe the United States would waver if confronted with the prospect of trading one ally in Tokyo to save another ally in Seoul. Or they might conclude that threats to Japan would lead Tokyo to deny US access to bases located on its territory for the defense of South Korea. Any daylight between the three countries surely emboldens North Korea, which is likely encouraged by the current state of trilateral relations and the open antagonism between Japan and South Korea.

Third, does North Korea believe the US-ROK alliance is credibly postured to fight and win a limited war under the nuclear shadow? North Korea may believe that holding hostage US and allied cities buys it an opportunity to wage conflict at lower levels. Its effort to deploy increasingly accurate and operationally flexible regional missiles, and the way it exercises them, suggest its leaders might even believe they can launch limited nuclear strikes without triggering an overwhelming allied response. Convincing North Korea that the alliance is willing and able to defeat aggression at any level of conflict must be a priority.

A fourth question stems primarily from developments off the peninsula: How does US-China competition shape North Korean perceptions of US commitments to South Korea? China remains North Korea’s most important patron and ally, whose military modernization and buildup is widely recognized. The 2018 US National Defense Strategy Commission concluded that the regional military balance has shifted to a point that the United States could suffer “unacceptably high” costs in a war with China that it “might struggle to win, or perhaps lose.” North Korean leaders might believe the United States would be unwilling or unable to defend South Korea if there is a credible threat of Chinese intervention. To date, there is little evidence the US-ROK alliance is developing combined measures to preclude such thinking.

Renewing US Commitments: Options and Opportunity

Should tensions with North Korea grow, US and allied leaders will face difficult tasks. Tending to the requirements of extended deterrence will be among the top priorities. The preceding section presented four areas where deficits may exist: perceptions of US resolve; trilateral cohesion; ability to fight a limited war under the nuclear shadow; and deterring/countering Chinese intervention.

Below is an exploration of options to fill potential gaps. It is important to keep in mind, however, there will likely be very different views in South Korea of what should be done and much will depend on which political party is in charge. The Moon administration has tended toward a softer deterrence posture to advance diplomatic relations with North Korea and China. Historically, liberal governments like the current one have been more wary of the alliance and invested in options that preserve freedom of action. The opposition party has pledged a harder line on North Korea and China. In the past, conservative governments have emphasized efforts to highlight the alliance’s combined deterrence posture and sought robust and tangible US commitments.

While only one of many tools, US nuclear weapons have long been a powerful instrument for signaling vital national interests and the resolve to defend them. Nuclear signals can provide high-profile expressions of political commitment to both accept and inflict terrible costs on behalf of an ally. There are three broad approaches for how leaders in Washington, as well as Seoul, might think about leveraging US nuclear forces in the future.

  • Status Quo Plus: The most modest approach would not involve major changes to existing arrangements. The United States would continue to rely on contiguous US (CONUS)-based capabilities, including the strategic deployment of bombers, to signal US commitment. The 2017 bomber overflight missions in which ROK and Japanese fighters provided tactical escort was a particularly strong show of unity. Building on, even routinizing, combined exercises of this kind could demonstrate both US resolve and alliance cohesion.

Other recent developments also provide new signaling opportunities. Earlier this year, the United States deployed a low-yield warhead option for its SLBMs. While characterized as a response to Russian doctrine and forces, this new capability could play a deterrence role against North Korea. It adds flexibility to US deterrence forces and offers potentially more credible response options in a narrow but critical set of scenarios. For instance, the 2018 Nuclear Posture Review calls for holding at risk North Korea’s leadership and missile force. Having a prompt, accurate and penetrating low-yield option against those types of targets in limited attack scenarios likely conveys more credibility than relying on much higher-yield weapons or much slower delivery systems. A visit to Guam by a US ballistic missile submarine (SSBN) carrying the new warhead would signal its presence and potential utility in the region. Inviting ROK and/or Japanese delegations to tour the boat could highlight common purpose among allies.

US leaders might also consider opportunities afforded by the recent change in regional strategic bomber operations. No longer will bombers be based in Guam. Rather, CONUS-based bomber groups will now utilize a broader array of locations to increase resiliency and operational flexibility. Conducting an early demonstration of the ability to deploy and operate from multiple locations would signal sustained US commitment and ability to fight more effectively in a limited nuclear conflict. There also are opportunities to demonstrate alliance cohesion. An official statement about the change said, “We will maximize all opportunities to train alongside our allies and partners, to build interoperability, and bolster our collective ability to be operationally unpredictable.” Perhaps that could involve joint exercises and investments in airfields, including on allied territory.

Lastly, the United States maintains mature high-level dialogues with South Korea and Japan that advance a common understanding of deterrence requirements, the role of US nuclear weapons and the value of policy coordination. Establishing a formal bilateral or trilateral operational-level nuclear crisis planning mechanism to support policy decisions could be an important next step to strengthen these relationships. The basic idea is to sustain attention on the operational implications of a North Korean nuclear attack as well as alliance mitigation and response options under a range of scenarios. The specific goal is to strengthen combined and coordinated conventional military planning under the nuclear shadow. If established, such an enhanced consultative process should reflect the reality that an effective response to a North Korean attack at any level will require a coordinated US-ROK-Japan approach. A trilateral nuclear crisis planning mechanism would strengthen planning and serve as a powerful deterrence signal.

  • Forward Deploy: A second, more controversial approach would involve deploying US nuclear weapons to South Korea. This is an option long favored by a majority of South Koreans—about 55-65 percent—in public opinion polls for over a decade as well as prominent politicians, although not by South Korean President Moon Jae-in. There is scant support for this course of action in the United States for many good reasons. The main reason is that it is militarily unnecessary because the current suite of US capabilities can destroy any target in North Korea. In addition, US nuclear weapons based in South Korea would be vulnerable to attack and, thus, unreliable as a response option. Finally, their presence would provide first strike incentives that contribute to crisis instability.[3]

Arguments against the deployment option are valid in their own right but do not necessarily vitiate the underlying deterrence logic. Namely, it is difficult to imagine—in a world of garbled messages—a clearer signal of US willingness to run nuclear risks to defend a vital interest than placing nuclear weapons in harm’s way. While this may not significantly enhance US military options, it certainly complicates North Korean targeting decisions for any attack in which it might hope to keep conflict limited. By increasing the perceived risk that any conflict would become a nuclear one, partly due to first strike incentives, North Korea may be persuaded that, in fact, it cannot wage a limited conflict and manage the risks of escalation.

It’s possible the financial costs and escalatory risks inherent in this option would outweigh the deterrence benefits. China would be sure to make such costs as high as possible, if its reaction to the deployment of THAAD in South Korea is any indication. At the same time, it is precisely such high-cost and high-stake measures that can send powerful strategic signals. Cheap and easy actions do not carry much weight.

To be sure, the debate over the deployment option is not going away. It is likely to grow in intensity in the coming years. Pressure is mounting in South Korea to develop an independent nuclear capability, if the United States does not take seriously perceived credibility gaps in the US nuclear “umbrella.” Few US strategists believe this would be a good outcome.

  • Phased and Adaptive: With that in mind, a third approach could adopt a phased, adaptive model. The United States could commit to deploying nuclear weapons to South Korea at some indeterminate time in response to a heightened North Korean threat, implementing a series of phased steps to create the necessary conditions and reduce the deployment timeline. For instance, a preparatory phase might include conducting a survey of potential storage locations and an environmental impact study. A subsequent phase could involve training combined US-ROK units to conduct perimeter security, incident response and recovery operations. A later phase could involve certifying Korea-based US F-16 units (or F-35 replacements) for nuclear missions and conducting combined exercises. A final phase would be the construction of storage facilities. Each step could be adapted to a changing security environment prior to putting actual US nuclear weapons in South Korea.

There are inevitable tradeoffs associated with this approach. Concretely conveying resolve but conditioning deployment on North Korea’s behavior could strengthen deterrence and incentivize restraint. Each phase offers an opportunity to signal and apply incremental pressure on the North while preserving flexibility to manage associated costs and risks. However, perceived half measures would belie resolve. A convincing commitment toward deployment would be necessary but has the potential to create unhelpful “tit-for-tat” expectations in which every North Korean provocation requires taking the next step. Drawing out the timeline also would invite pressure from China, Russia and domestic audiences to abandon the option. Pushing forward in the face of associated costs could reaffirm the perception of resolve but ultimately may come at a higher price than a “deploy now” option. Optimistically, if China and Russia see that deploying US nuclear weapons to South Korea is a serious option, they might apply more pressure to restrain North Korea.

The US-ROK alliance could also take conventional measures to strengthen extended deterrence. For one, it could resume large-scale military exercises after a long pause to signal strategic and operational readiness. Sustained investments toward an integrated missile defeat capability—both left- and right- of launch—can deny North Korea the benefits it seeks from its missile force. Establishing a combined element to advance and align growing strike and missile defense capabilities would signal commitment to that mission. Integrating new nonkinetic capabilities, such as cyber and electromagnetic warfare, can expand the range of alliance options and reinforce deterrence objectives. Moreover, the alliance could take measures to demonstrate operational flexibility and resiliency necessary for fighting a limited nuclear war, including the ability to disperse and operate using a diverse range of ports and air bases. Should exercises involve locations in Japan, it would be a stronger message of trilateral unity.

Lastly, the US-ROK alliance could address Chinese pressure on extended deterrence by establishing a bilateral China policy coordination mechanism. This could be a valuable first step to signal Beijing and begin to strengthen response options against any effort to split the alliance. The United States is already investing heavily to maintain access to allies in the face of China’s growing regional power. But Washington has made clear those allies must contribute in meaningful ways in a new era of global competition. South Korea, a formidable high-tech ally, has much to offer in this regard. However, the alliance and ROK military investments have largely neglected China. Strengthening combined policies and military planning for third-party intervention could disabuse China and North Korea from concluding the United States might be unwilling or unable to defend South Korea. A turn of this kind toward Beijing would likely be extremely difficult for leaders in Seoul, but a failure to do so risks weakening deterrence on the peninsula.


As US and allied leaders consider how to respond to potential tensions with North Korea, they arguably face more challenging circumstances than two years ago. Demonstrating resolve may be a heavier lift largely due to North Korea’s and China’s growing capabilities. Fortunately, the allies have many tools and options for renewing US commitments. Each has costs and risks that must be weighed against expected deterrence benefits. None offers a silver bullet. The challenges discussed in this paper cannot be solved, only managed; they will require sustained attention and collective determination for the foreseeable future.

  1. [1]

    The views expressed here are solely those of the author and are not the policies or positions of National Defense University, the Department of Defense or any part of the US government.

  2. [2]

    Shane Smith, “Nuclear Weapons and North Korean Foreign Policy,” in North Korea Handbook, ed. Adrian Buzo  (New York: Routledge Press, forthcoming).

  3. [3]

    See: Richard Sokolsky, “The Folly of Deploying US Tactical Nuclear Weapons to South Korea,” 38 North, December 1, 2017,; and Jon Wolfsthal and Toby Dalton, “Seven Reasons Why Putting U.S. Nukes Back in South Korea Is a Terrible Idea,” Foreign Policy, October 11, 2017,

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