Promises under Pressure: Statements of Reassurance in US Alliances

The United States frequently reassures allies of its protection by stationing troops abroad, visiting allied countries, and making public statements. Yet the causes of reassurance in asymmetric alliances-those between a great power patron and its weaker allies-are understudied in the academic literature. Indeed, many scholars argue that reassurance can be counterproductive as it invites allies to free ride or provoke their adversaries, knowing that they have their patron's support. Despite the drawbacks, I argue that the United States use reassurance to discourage their allies from seeking outside options and reducing their dependence on the alliance. Patrons such as the United States thus face a dilemma wherein they trade-off between withholding reassurance for short-term leverage and using reassurance to preserve their long-term influence. I test the theory using a new cross-national dataset of US. statements of reassurance from 1950 to 2010, and the results provide stronger support for my hypotheses than for the competing explanations of deterrence, strength from desperation, and shared preferences. The findings have implications for understanding how great powers manage their alliances, and suggest a pathway through which weaker states can shape great powers' foreign commitments.