Deterrence, reassurance, and can kicking: The Washington Declaration

On April 26, the United States and South Korea marked the 70th anniversary of their alliance by announcing the Washington Declaration, which opens a new chapter in the alliance’s approach to extended deterrence. South Korea expressed its “full confidence” in U.S. commitments and reaffirmed that it will not pursue its own nuclear weapons in exchange for greater high-level participation in U.S. nuclear planning to respond to North Korea.

The Washington Declaration never mentions the word “reassurance,” but the policies it sets forth are much better understood as reassurance measures rather than deterrence measures. Moreover, the new declaration will do nothing to resolve the underlying forces that prompted its creation in the first place.

The phrase “extended deterrence” describes the U.S. using its nuclear arsenal to prevent attacks against its allies. Extended deterrence has an important nonproliferation component as well, as the protection offered by U.S. nuclear weapons is supposed to dissuade allies from acquiring their own nuclear weapons. On the modern-day Korean peninsula, U.S. extended deterrence is primarily geared toward preventing a North Korean attack, nuclear or conventional, against South Korea.

A perennial challenge to U.S. extended deterrence commitments is the credibility problem. When the U.S. extends its nuclear umbrella it is making a promise to use its nuclear weapons to protect territory that is not its own.

That is a very bold claim to make, especially when the threatening country—in this case North Korea—can threaten U.S. territory with nuclear attack. Allies understandably fear that if push came to shove, the U.S. may not make good on its promises since its territory is not at stake. Reassuring allies that the U.S. will live up to its commitments is thus an important part of extended deterrence, and arguably more difficult than deterring the adversary.

The dynamics on the Korean peninsula leading up to the Washington Declaration illustrate how reassurance is difficult even if deterrence is easy. Preventing a North Korean attack against South Korea should be straightforward. The U.S. and South Korea field large and very capable militaries, and the U.S. has a massive advantage over North Korea in nuclear forces. Pyongyang knows that it is in a much weaker position, that it cannot hope to survive against a concerted effort to destroy it, and it has leaned heavily into a nuclear strategy that emphasizes going first and going quickly if it detected an imminent attack. 

In January 2021, North Korea held a major meeting of the ruling Workers’ Party in which Kim Jong-un set forth a plan to add new types of capabilities to the country’s nuclear arsenal. The next year saw a worsening spiral of tension on the peninsula. North Korea started testing more missiles, Seoul and Washington restarted large-scale military exercises that were previously halted to incentivize diplomacy, and Pyongyang responded with even more missile activity. In January 2023, South Korea’s president Yoon Suk-yeol said continued North Korean provocations could prompt Seoul to acquire nuclear weapons or push the U.S. to strengthen its extended deterrence commitment.

The Washington Declaration is an attempt to satiate South Korea’s desire for stronger reassurances from the U.S. and put recent calls for a South Korean nuclear weapon to rest. It will probably work, but the question is for how long.

The declaration mentions displays of U.S. “strategic assets” such as an upcoming port visit of a ballistic missile submarine to South Korea. These displays are likely to prompt a strong North Korean reaction based on the North’s recent behavior of reacting to joint U.S.-South Korea military drills with their own missile exercises. The consultative procedures established in the Washington Declaration might prevent a tit-for-tat escalation in tensions that forces Seoul to seek even more reassurances, but it is not a foregone conclusion.

The Washington Declaration treats a symptom but not the underlying disease. Without constraints on North Korea’s nuclear program, Kim Jong-un will continue to expand his arsenal, which, in turn, will undermine credibility in U.S. extended deterrence commitments and prompt South Korea to seek more reassurances. Staying stuck on the treadmill of constant reassurances would be familiar to the U.S., but it is not a good use of U.S. power over the long term.

Instead of trying to fill the bottomless pit of reassuring South Korea, the U.S. should back down from its unrealistic expectation of denuclearizing North Korea and instead attempt to restrain Kim’s nuclear arsenal via arms control. This would be a difficult process, to be sure, but without a course correction the Washington Declaration will only kick the can of reassurance down the road until the next crisis of confidence in U.S. extended deterrence commitments.

Eric Gomez is a senior fellow at the Cato Institute.