North Korea has been vastly increasing its nuclear weapon threat and plans to accelerate this process in the future. North Korea has also adopted an extremely hostile campaign of threatening the Republic of Korea (ROK) and the United States with nuclear attacks. China is also vastly increasing its nuclear weapon capabilities and is no longer trusted by most people in the ROK.

To counter these threats, the United States provides extended deterrence for the ROK and promises a nuclear umbrella to cover the ROK so that the ROK does not need its own nuclear weapons. The United States wants a nuclear weapon–free Korean Peninsula to avoid imperiling the Nuclear Non-Proliferation Treaty, the foundation of U.S. nuclear nonproliferation policy. The United States has constructed its nuclear umbrella on a high degree of strategic ambiguity in the belief that this ambiguity will achieve the most-effective deterrence of North Korean aggression.

But this ambiguity, the growing North Korean threat, and U.S. withdrawal from other allied countries (e.g., Afghanistan) have caused many in the ROK to question the existing U.S. commitment and seek more-concrete assurance. Sensitive to this concern, President Joe Biden supported ROK President Suk Yeol Yoon with the Washington Declaration in April 2023. This report proposes options that the United States and the ROK could exercise to strengthen ROK nuclear assurance consistent with the Washington Declaration, including enhancing strategic clarity, coercing North Korea to freeze its nuclear weapons, and committing U.S. nuclear weapons to support the ROK.