A Measure for Crisis Instability with an Application to Space-Based Antimissile Systems

Crisis instability is the danger of war due to each side's fear that the other is about to attack. An index is defined to measure the degree of instability in a situation and is justified by a set of persuasive criteria that any such measure should satisfy, and also by a set of axioms based in the theory of games. Some past measures are summarized and compared.In the second part, we give a simple quantitative model of a nuclear exchange and look at the stability consequences of changing various weapons parameters and of adding a space-based missile defense system, with and without submarines. Defenses tend to harm stability unless they are both very large and designed so that the government that strikes first does not have a relative advantage in attacking the opponent's defenses.