Missile defense

US ballistic missile defenses, 2019

Missile defense systems can have a significant effect on nuclear weapons postures, the strategy for their potential use, and crisis stability and international security. The defenses don’t even have to work very well; the uncertainty that they might work, or could become more capable in the future, are enough to trigger the effect. Advocates argue that missile defenses don’t threaten anyone and can help deter adversaries, but those adversaries are unlikely to simply give up; they are more likely to be stimulated to try to beat the defenses to ensure their own deterrent forces remain effective and credible. This dynamic is clear from many cases during the Cold War and remains evident today. On balance, it is difficult to see what real national security benefits the United States has achieved from decades of missile defense research and development. While defense of a forward base of a limited size may be possible, the promise of a credible defense of the homeland remains doubtful. Instead of assured security, missile defenses have helped to harden adversarial perceptions of US intentions and fueled development of more capable offensive capabilities directed against the United States and its allies. In response to actual or suspected missile defense capabilities, the nuclear-armed states undertook substantial modernization programs during the Cold War.