Alliance formation and national security

The premise that nations form alliances in order to improve their security is widespread in the study of international relations. Yet in spite of the crucial role played by this assumption, the claims of policy makers and statesmen form our only evidence that it is the need for greater national security which motivates the formation of alliances. What is more, we have no systematic evidence that the concern for national security would be a consistent predictor in the face of other plausible goals. Our intent in this paper is to supply this evidence.

From the assumption that greater national security is a primary incentive to form an alliance, we construct a series of hypotheses, each building successively on the previous hypothesis to predict conditions at the individual, dyadic and systemic levels of analysis. By constructing an indicator of national security, we are able to test these hypotheses against historical information about European alliances from 1815 to 1965. Our evidence that security considerations are indeed central to alliance behavior improves the empirical and theoretical foundation of a considerable body of studies in international relations and foreign policy preceding this one.