Domestic political instability provides an incentive for external military intervention by raising the opportunity costs of nonintervention. When deciding to intervene in response to instability within its sphere of influence, a regional hegemon considers the anticipated actions of other potential interveners. In particular, a hegemon has an incentive to intervene preemptively to forestall future interventions by rival powers. Given this, military intervention will be more likely when another power provides an external threat to a hegemon’s sphere of influence. A historical examination of U.S. intervention policy and behavior in the Caribbean Basin supports the theory.
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