The End of Balance-of-Power Theory? A Comment on Wohlforth et al.’s ‘Testing Balance-of-Power Theory in World History’ METTE EILSTRUP-SANGIOVANNI University of Cambridge, UK The balance of power is one of the oldest and most venerable concepts in the study of International Relations. Few concepts have had a comparable influence on both scholarship and statesmanship, and few have been so fiercely contested. In a recent article, ‘Testing Balance-of- Power Theory in World History’ ( EJIR, June 2007), Wohlforth et al. set out to test balance-of-power theory against 2000 years of world history. Although their article has considerable merits, I highlight three main weaknesses in their approach. First, I argue that they misstate balance- of-power theory. Second, the competing theoretical hypotheses they offer are (a) not novel, (b) too vague to enable productive empirical testing. Third, the historical evidence they present, based on the study of ancient international systems, is too scant and impressionistic to be probative for the causal mechanisms they seek to evaluate. As a result, balance-of-power theory is neither refuted nor significantly refined. KEY WORDS ♦ balance-of-power theory ♦ neo-classical realism ♦ neorealism ♦ world history Introduction The balance of power is one of the oldest and most venerable concepts in the study of International Relations. Few concepts have had a comparable influence on both scholarship and statesmanship, and few have been so fiercely contested. In a recent article, ‘Testing Balance-of-Power Theory in World History’ ( EJIR, June 2007),1 Wohlforth et al. (or the ‘Wohlforth European Journal of International Relations 15(2) 348 team’) once again confront the balance of power. Noting that the concept is as central in today’s scholarship as it has been at any time since the Enlightenment (p. 156), they set out to ‘test the balance of power’ against evidence from eight international systems over 2000 years of world history. The core proposition that they evaluate is that ‘balancing behaviour prevents systemic hegemony’. Their findings — chiefly that the effectiveness of balancing is frequently undermined by collective action problems, by emulation failure or by uncertainty, and that hegemonies are habitually allowed to form — fatally undermines, so they claim, the core propositions of balance-of-power (BoP) European Journal of International Relations Copyright © 2009 SAGE Publications and ECPR-European Consortium for Political Research, Vol. 15(2): 347–380 [DOI: 10.1177/1354066109103145]