This post is authored by Adam Mount, senior fellow and director of the defense posture project at the Federation of American Scientists. It is part of a project conducted by the program on U.S.-Korea policy at the Council on Foreign Relations, supported by the Smith Richardson Foundation and Korea Foundation. This series of posts addresses the U.S. nuclear posture in Northeast Asia, implications of North Korean nuclear and missile programs for U.S. extended deterrence commitments, operational and tactical dimensions of deterrence on the peninsula, and regional dimensions of stability. To further stimulate an open discussion of these issues, we would like to invite reader responses. Please contact Ellen Swicord at eswicord@cfr.org for submission guidelines if you are interested in contributing a response.

In retrospect, 2017 marked an inflection point for North Korea’s missile arsenals. Before that point, Pyongyang gradually advanced a handful of rudimentary and unreliable systems. Since then, a new generation of systems, which have proven far more capable and reliable, have superseded many of the earlier systems. Though many have been tested only once or twice, Pyongyang has sought to communicate that several of its new generation systems possess advanced capabilities that present a significant challenge to the deterrence posture of the U.S.-South Korean alliance. North Korea’s advancements are one of several regional developments that are piling up unaddressed on the U.S.-South Korean deterrence agenda.

Consider one recent example of a North Korean advancement that will complicate allied planning. Since May, North Korea has begun testing the KN23 , a remarkably advanced short-range ballistic missile. First displayed in 2017, the system has reportedly demonstrated the ability to maneuver in flight along a depressed trajectory (a deliberately low flight path). These capabilities together imply that the missile can reach its target faster and complicate the task of the U.S. and South Korean missile defenses that would attempt to intercept it.

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In a July statement announcing the KN23 tests, Pyongyang justified them as a response to “ultra-modern weapons and equipment which the bellicose forces of the south Korean military are introducing,” which the regime characterizes as “definitely offensive weapons.” The passages likely refer to South Korea’s acceptance of two additional F-35 stealth aircraft two weeks prior, which Pyongyang worries could penetrate its air defenses and strike its leadership or missile forces without warning. Unable to prevent or prepare for a strike, the regime has apparently taken other measures. The new missiles, the statement said, are capable of “neutralizing those weapons…turning them to scrap iron at an early stage when it is considered necessary.” In other words, the new missile represents a first strike option to destroy stealth aircraft on the ground before they have a chance to take off, or potentially to destroy the command and control networks that coordinate military operations.

The KN23 signals an alarming evolution in North Korea’s strategic thinking. North Korea has moved beyond rudimentary forces that could retaliate for an attack or attempt to prevent U.S. reinforcements from arriving on the peninsula in a major war. The regime is signaling not only that it would act early in a crisis to prevent a war from escalating out of its control, but also that it would attack allied leadership, command networks, missile defense batteries, or aircraft on the peninsula to degrade South Korea’s will or ability to continue the fight. If used in this way, KN23 might represent a form of escalation control.

Ongoing testing affords Pyongyang an invaluable opportunity to increase its confidence that these systems will work as intended in a conflict, and to test different trajectories and maneuvers. Without successive tests, the regime would likely lack confidence that the missiles could sustain the stresses of depressed trajectories or successfully control their maneuvers, and would be more hesitant to use them.

The KN23 is just one of the major advancements North Korea has demonstrated since 2017. Before the current round of negotiations began, the regime tested one intermediate-range and two intercontinental-range ballistic missiles. In that time, it also demonstrated a medium-range solid-fuel ballistic missile, maneuverable reentry vehicles on short-range SCUD missiles, and a large-diameter multiple-launch rocket system capable of flying depressed trajectories.

In short, since the Trump and Moon administrations came into office, North Korea has demonstrated a new generation of missile forces. It has made both qualitative advancements (the ability to fire more missiles faster to longer range) and quantitative advancements (the ability to rapidly strike defended targets preemptively or preventively). Both will require adaptations to U.S.-ROK alliance planning.

In addition to North Korea’s developments, this summer has been a watershed moment for trends that threaten to compromise South Korea’s place in the region. In July, South Korean aircraft fired warning shots after a Russian bomber after it entered the airspace of islands administered by South Korea in a joint operation with Chinese aircraft. In early August, China warned against deployment of U.S. intermediate-range systems to Asia, including to South Korea, threatening “countermeasures” that could restart the economic coercion campaign it applied in response to the alliance’s deployment of a THAAD missile defense system, which lasted over a year. Japan has also removed South Korea from a white list of favored trading partners and applied coercive economic pressure in response to ongoing disputes over history issues.

These developments have added considerably to the U.S.-ROK alliance agenda, and U.S. and South Korean leaders must now grapple with several critical questions, including:

How does North Korea’s acquisition of an ability to target the continental United States change contingency planning, if at all?

How and when should the alliance plan to strike against the regime’s leadership, against its nuclear forces, and in response to limited North Korean aggression? How should the alliance communicate the costs of aggression to North Korea? Prior to the modification of joint exercises in support of diplomacy, public events implied a growing disparity in how the allies viewed these questions.

How should the alliance understand and respond to North Korean strikes against military targets far from hostilities early in a crisis? Should these strikes be understood as horizontal escalation, or coercive, preemptive, or preventive attacks? How should the alliance respond, especially if the strikes degrade missile defense, command and control, or tactical aviation capabilities?

What are Seoul and Washington’s requirements for a minimum acceptable condition of stability on the peninsula? What are their priorities given an opportunity to place partial caps on North Korea’s nuclear program? And how can both be coordinated with Tokyo’s preferences?

What is the plan for the future of joint exercises on the peninsula?

What is the future of cost-sharing arrangements with South Korea after the Trump administration’s unreasonable demands for steep increases in its contributions?

What role should the United States play in contingencies resulting from foreign incursions into ROK airspace and territorial waters?

How can the alliance deter economic coercion or help to mitigate its effects?

Their respective negotiations with North Korea have led the United States and South Korea to paper over several challenges facing the alliance. Both Seoul and Washington have chosen to present an optimistic assessment of negotiations and the alliance, rather than to undertake the difficult conversations necessary to develop a sustainable strategy to manage a nuclear-armed North Korea.

If and when negotiations collapse, the United States and South Korea will likely face a North Korea that is far more capable than before, in a region that has become far more hostile to South Korean interests. The sooner the alliance starts working through challenges on the agenda, the stronger it will be.