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The article develops an expected-utility model of extended deterrence and tests it on 54 historical cases. Successful deterrence is associated with close economic and political ties between the defender and the state it is trying to protect, and with a local military balance in favor of the defender. Deterrence success is not systematically associated with the presence of a military alliance, with the overall strategic military balance, with possession of nuclear weapons, or with the defender's firmness or lack of it in previous crises. If deterrence fails, only alliance and the military value of the state under attack are associated with the defender's willingness to go to war.
Huth et al. (Sun,) studied this question.