Testing Balance-of-Power Theory in World History

The balance of power is one of the most influential theoretical ideas in international relations, but it has not yet been tested systematically in international systems other than modern Europe and its global successor. This article is the product of a collective and multidisciplinary research effort to redress this deficiency. We report findings from eight new case studies on balancing and balancing failure in different international systems that comprise over 2000 years of international politics. Our findings are inconsistent with any theory that predicts a tendency of international systems toward balance. The factors that best account for variation between balance and hegemony within and across international systems lie outside all recent renditions of balance-of-power theory and indeed, international relations scholarship more generally. Our findings suggest a potentially productive way to reframe research on both the European and contemporary international systems.