Collective Deterrence

Abstract

We analyze a model of collective deterrence in which (1) one state may challenge a status quo defended by a great power and an arbitrary number of partners and (2) defender war costs are private information. We show first that the great power’s intra-coalition dominance shapes which cooperative failure, free riding, or uncertainty over others’ willingness to fight may weaken deterrence. Second, increasing the great power’s war payoffs increases both deterrence and partner free riding. Third, the extent of great power dominance determines whether a larger or more capable coalition enhances or weakens deterrence and ensures that size and capabilities work in opposite directions. Finally, increasing uncertainty over a great power’s war costs can decrease or increase deterrence, depending on the prior strength of its commitment. We also use the model to illuminate differing responses of American allies in Europe and East Asia to the 2016 election of Donald Trump.