How Enemies Become Friends: The Sources of Stable Peace, Charles A. Kupchan (Princeton, N.J.: Princeton University Press, 2010), 448 pp., $29.95 cloth.

The transition from enmity to halting cooperation and, eventually, to lasting friendship between states begins, according to Charles Kupchan, “amid peril.” Faced with multiple strategic threats and a scarcity of the resources necessary to counter them, a state gambles on a unilateral offer of an outstretched hand to an adversary. If the offer is rebuffed, the parties return to geopolitical rivalry, which is, after all, the default setting of international relations. If, on the other hand, the offer is read as a genuine invitation to a handshake (rather than, say, a duplicitous scheme for delivering a sucker punch), the two countries can begin to move down the delicate path toward stable peace—the defining characteristic of which is the banishment of armed conflict from the tool kit of legitimate statecraft.

Loyalists to one or another school of international relations may chafe at this ambitious and conceptually diverse work of stable peace theory-building. Kupchan—a professor of international relations at Georgetown and Senior Fellow at the Council on Foreign Relations—draws explicitly, and eclectically, from a variety of theoretical sources, and the result is an appropriately nuanced account of peacemaking that smartly frustrates traditional boundaries. Although the onset of stable peace is best described by realism, as is the pervasive nature of geopolitical competition in general, the fact that international anarchy can give way to “international society” at all, and that this process is nurtured by the institutionalization of rules and norms and a commitment to reciprocity, is well accounted for by liberal theory. Constructivist ideas about identity and the formation of cultural narratives, meanwhile, provide crucial sociological insights into the shift in political discourse that precipitates the consolidation of stable peace.

The bulk of the book is given over to some twenty case studies, dating from the thirteenth century to the present, and along the way Kupchan's clear and studious analysis calls into question the supremacy of various theories of international relations. As such cases as the Concert of Europe or, more recently, the Association of Southeast Asian Nations demonstrate, non-democracies are in fact capable of making peace with their rivals. A regime's behavior, Kupchan argues, indicates better than its type its potential as a partner for peace. Perhaps most counterintuitively, Kupchan finds that, prevailing wisdom to the contrary, political reconciliation must first clear the way for economic interdependence to have any meaningful effect on interstate relations. “Diplomacy,” stresses Kupchan, “not trade or investment, is the currency of peace.”