Reevaluating Alliance Reliability

Previously reported empirical evidence suggests that when conflict arises, military alliances are not reliable; state leaders should only expect their alliance partners to join them in war about 25% of the time. Yet, theoretical arguments explaining the choices of leaders to form cooperative agreements are at odds with such empirical evidence. This puzzling gap between theory and evidence motivates a reconsideration of previous measures of alliance reliability. Many alliance treaties include specific language regarding the circumstances under which the alliance comes into effect, often limiting obligations to disputes with specific target states or in specific geographic areas, and many treaties do not go so far as to require states to join in active fighting. Considering the specific obligations included in alliance agreements provides an improved estimate of the propensity of states to honor their commitments. Results show that alliances are reliable 74.5% of the time.