►Nuclear weapons are assuming new salience for security dynamics in East Asia and on the Korean Peninsula. North Korea's nuclear weapons program continues to advance. China appears to be accelerating a long-running nuclear modernization and expansion program. In the past few years, China has deployed new advanced nuclear-capable systems.

►The state of deterrence on the Korean Peninsula appears strong. North Korea’s short-term motivation for unification is low, U.S. military commitments to South Korea are clear, and the military balance on the Peninsula strongly favors the U.S.-South Korean alliance.

► How can we understand these dynamics and what do they suggest for direct and extended deterrence on the Korean Peninsula? How is the intensifying nuclear competition in East Asia likely to play out?

Nuclear weapons are assuming new salience for security dynamics in East Asia and on the Korean Peninsula. North Korea’s nuclear weapons program continues to advance. This year, North Korea ended its four-year moratorium on testing intercontinental ballistic missiles (ICBMs) and, as of mid-October, had carried out at least 40 missile tests in 2022 alone, the most in any year so far. North Korea claims to have tested a missile with new hypersonic capabilities and alleges it has deployed cruise missiles capable of carrying “tactical nukes.” Prominent open source estimates assess that North Korea is gradually expanding the size of its nuclear arsenal and that the country “might have produced sufficient fissile material to build 45 to 55 nuclear weapons and might have assembled 20 to 30 warheads for delivery primarily by medium-range ballistic missiles.”

China appears to be accelerating a long-running nuclear modernization and expansion program. In the past few years, China has deployed new advanced nuclear-capable systems including the DF-17 medium-range ballistic missile with hypersonic glide vehicle and both the DF-31AG DF-41 road-mobile ICBMs. The Department of Defense estimates that China may have up to 700 deliverable nuclear warheads by 2027 and that China “likely intends to have at least 1,000 warheads by 2030.”

Against this backdrop, debates about nuclear policy in both South Korea and the United States have intensified. Polling data from the Seoul National University Institute for Peace and Unification Studies reveal that South Koreans feel increasingly threatened by North Korea’s nuclear weapons. Large majorities of South Koreans now report favoring both the redeployment of U.S. nuclear weapons to South Korean territory or South Korea’s development of its own nuclear weapons capabilities. Officials in South Korea and Japan called for the hosting of U.S. nuclear weapons and U.S. observers have called for new nuclear capabilities to counter China’s.

How can we understand these dynamics and what do they suggest for direct and extended deterrence on the Korean Peninsula? How is the intensifying nuclear competition in East Asia likely to play out?

Lessons from the Literature

Although some of the recent nuclear developments in East Asia and on the Korean Peninsula are new, the security studies literature offers several lessons for how to understand them. First, recent research, including work examining the experience of regional nuclear powers like North Korea, shows that the relative nuclear balance does not matter much for interstate bargaining, so long as both states enjoy survivable second strikes. Instead, the way an arsenal postured matters most for deterrence dynamics. In particular, arsenals postured for a strategy of “asymmetric escalation” are particularly effective at deterring aggression. An asymmetric escalation strategy “is explicitly designed to deter conventional attacks by enabling a state to respond with rapid, asymmetric escalation to the first use of nuclear weapons against conventional and/or strategic targets.” However, it is precisely because of the higher risks of nuclear escalation that these strategies are more effective. By contrast, strategies of “assured retaliation,” in which nuclear weapons are placed under centralized control and intended to only deter and retaliate against nuclear strikes, are likely to be less escalatory, especially in a crisis.

Therefore, it matters not precisely how many nuclear weapons North Korea deploys but, rather, what North Korea does with those weapons. Specifically, does the country deploy low-yield tactical nuclear weapons to frontline military units entrusted with first-use launch authority or does it deploy large-yield weapons postured for survivability and subject to strict central control? North Korea’s nuclear strategy remains unclear and some scholars have described it as deliberately ambiguous and featuring elements of various strategies. For instance, North Korean statements about the possibility of nuclear first use are vague and contradictory, though the country’s recent nuclear law, passed in September 2022, outlines several circumstances under which the country might use nuclear weapons first. Similarly, while the country’s early warhead designs were heavy and unsuitable for so-called tactical delivery vehicles, recent North Korean reports claim the deployment of cruise missiles is suitable for tactical nuclear weapons. While the country’s highly controlled political system would complicate pre-delegation of launch authority, questions about the nuclear force’s survivability incentivize rapid launches.

While an explicit move in North Korean toward an asymmetric nuclear posture predicated on early first use would likely be destabilizing, the ambiguities in its current nuclear posture can also be dangerous. Ambiguity and misperception about North Korea’s nuclear intent and behavior may make nuclear escalation in a crisis or conflict more likely.

Second, the record suggests that while nuclear weapons are not especially effective at enabling large-scale conventional aggression, they may support more limited offensive actions. Research suggests that nuclear weapons are best at deterring aggression but not at conquering territory. Nuclear weapons are relatively blunt instruments ineffective at taking or holding territory; indeed, they will often destroy what might otherwise be conquered. However, nuclear weapons may encourage violence at lower levels of intensity, especially if both sides are nuclear-armed. The “stability-instability paradox,” for instance, argues that, when there is relative “stability” at the nuclear level, sometimes meaning mutual nuclear vulnerability, there may be greater instability at conventional levels as a revisionist actor engages in lower-level provocations behind its nuclear shield.

These dynamics might influence North Korean military “gray zone” actions. As North Korean nuclear capabilities advance, they may encourage North Korean adventurism such as “campaigns involve the gradual application of instruments of power to achieve incremental progress without triggering a decisive military response.” This could include increased cyber operations, maritime aggression near the Northern Line Limit, hostile actions along the Demilitarized Zone (DMZ), and provocative nuclear or missile tests.

Third, recent developments suggest a weakening of the constraints around using or threatening to use nuclear weapons, including the nuclear taboo. Past research has suggested that a nuclear taboo inhibited leaders from threatening or using nuclear weapons. However, that taboo may be weakening. Russia’s invasion of Ukraine and its ambiguous nuclear threats are likely to further weaken the nuclear taboo and may encourage other countries, such as China and North Korea, to enhance the role of nuclear forces in their national security strategies. Indeed, some Chinese strategists have argued that “Russia achieved the coercive benefits of nuclear signaling without issuing an explicit threat to use nuclear weapons.” North Korean observers may have learned the same. Chinese military and civilian national security analysts have argued events surrounding the conflict in Ukraine such as speculation that Belarus might revise its constitution to host nuclear weapons, risks to the Zaporizhzhia nuclear power plant, and Russian nuclear signaling have all eroded the nuclear taboo and loosened constraints on the use of nuclear weapons. Although Russia’s nuclear threats have remained ambiguous, they have still raised fears in the United States and Europe, illustrating the ability of even hints of nuclear use to heighten risks.

It’s admittedly unclear whether a country like North Korea would normally feel inhibited by a nuclear taboo. States which concentrate power in a single individual are more likely to pursue nuclear weapons and highly personalist leaders which also oversee widespread domestic human rights abuses like Kim Jong-un may otherwise be less inhibited from nuclear use for normative reasons. Still, global attitudes about the likelihood of nuclear use appear to be changing in dangerous ways which could further heighten risks on the Korean Peninsula.

Fourth, nuclear crises can be especially uncontrollable and dangerous. The time and decision constraints of interstate crises already inhibit clear decision-making; nuclear weapons can exacerbate these dynamics. A potential crisis involving both the United States and North Korea could resemble what some scholars have dubbed the “firestorm” model in which there are both low levels of controllability and high incentives for deliberate nuclear first use. This is because of the tremendous nuclear asymmetry between North Korea and the United States, which increases first-use incentives on both sides. Such a crisis would also have limited controllability because of uncertain North Korean nuclear command and control structures, the lack of mutually understood red lines, and few avenues for effective crisis communication. In this kind of crisis, the risks of nuclear escalation are highest. This is particularly due to the use-or-lose pressures that North Korea would confront due to its small and (likely) vulnerable nuclear arsenal. In a crisis, South Korea and the United States might be tempted to eliminate North Korea’s nuclear forces before they could be used; at the same time, North Korea, aware of these pressures, would be incentivized to use them.

Conclusion and Implications

These findings about nuclear dynamics in Northeast Asia and on the Korean Peninsula suggest implications for these challenges.

First, South Korea and the United States should, to the extent possible, discourage incentives for the first use of nuclear weapons. Asymmetric escalation postures, though effective at deterring, can introduce dangerous first-use incentives on both sides. Admittedly, there will be little room for directly influencing North Korean nuclear strategy but policies that decrease incentives for North Korean first use and enhancing mechanisms for crisis controllability—such as expanding the decision-making time available in a crisis, developing avenues for crisis communication, clarifying red lines, or reducing the extent North Korean leadership perceives use-or-lose pressures on their nuclear forces—may help reduce these risks.

Second, officials in both South Korea and the United States should emphasize minimizing the outbreak of crises. As discussed above, a nuclear crisis on the Korean Peninsula would be incredibly dangerous. The United States and South Korea should prioritize freezing North Korean missile and nuclear tests rather than rolling back existing capabilities. Not only will continued warhead design and missile testing bolster North Korean nuclear capabilities, but tests themselves can trigger dangerous international crises. Similarly, the South Korean and U.S. militaries should be sensitive to escalation dynamics. Research has shown that “North Korea views [joint military exercises] as a serious threat to its security” and that “[i]n response to a [joint military exercise], North Korea can issue warnings or threats as well as take costly signals such as conducting missile or nuclear tests.” While these exercises are important for ensuring cross-national interoperability, maintaining military readiness, and demonstrating alliance resolve and cohesions, they should be conducted in ways that minimize the offensive threat they are seen to pose.

Third, both South Korea and the United States should emphasize conventional capabilities over nuclear ones. While North Korea’s nuclear weapons can support deterrence and gray zone activities, it is the country’s conventional capabilities that would constitute any invasion force. Emphasizing the nuclear dimension of security guarantees can even backfire, raising concerns in South Korea of nuclear escalation and increasing support for nuclear proliferation among South Koreans. Reducing nuclear salience on the Korean Peninsula may also help diminish North  Korean incentives for nuclear first use. Conventional capabilities are also better suited for countering gray zone activities. Officials can also work to both strengthen the nuclear taboo and signal that Russian nuclear signaling will not be effective in order to reduce the attractiveness of similar signaling by North Korea.

The state of deterrence on the Korean Peninsula appears strong. North Korea’s short-term motivation for unification is low, U.S. military commitments to South Korea are clear, and the military balance on the Peninsula strongly favors the U.S.-South Korean alliance. However, accidents and misperceptions can threaten to both cause and escalate crises. Nuclear weapons heighten these dynamics. Managing these issues will be challenging but learning from nuclear experiences elsewhere can guide policymaking to maximize peace and stability on the Korean Peninsula.