Published in International Security, Vol. 46, No. 3 (Winter 2021/22), pp. 51–86
North Korea has made significant strides in its attempt to acquire a strategic nuclear deterrent. In 2017, it tested intercontinental ballistic missiles (ICBMs) and completed a series of nuclear test explosions. These may provide North Korea with the technical foundation to deploy a nuclear-armed ICBM capable of striking the United States. The Ground-based Midcourse Defense (GMD) missile defense system is intended to deter North Korean nuclear coercion and, if deterrence fails, to defeat a limited North Korean attack. Despite two decades of dedicated and costly efforts, however, the GMD system remains unproven and unreliable. It has not demonstrated an ability to defeat the relatively simple and inexpensive countermeasures that North Korea can field. The GMD system has suffered persistent delays, substantial cost increases, and repeated program failures because of the politically motivated rush to deploy in the 1990s. But GMD and other U.S. missile defense efforts have provoked serious concerns in Russia and China, who fear it may threaten their nuclear deterrents. Diplomacy and deterrence may reassure Russia and China while constraining North Korea's nuclear program. An alternate airborne boost-phase intercept system may offer meaningful defense against North Korean missiles without threatening the Russian or Chinese deterrents.