As Darnton notes, parochial bureaucratic interests -- particularly within security forces that rely on perceptions of enduring external threats to justify their influence and incomes -- can act as major obstacles to reconciliation between rival states. What, then, explains the rapprochements between traditional pairs of rivals such as Argentina and Brazil, Argentina and Chile, or Honduras and Nicaragua? Darnton identifies two conditions that have made such détentes possible: the emergence of alternative threats such as domestic insurgencies and tight budget constraints that compel security forces to forgo preparations for external wars in favor of counterinsurgency at home. Darnton does not overstate his case and recognizes that there are other paths to peace. Darnton warns U.S. policymakers that too much foreign assistance to security forces might inadvertently delay reconciliation between two rivals that are both U.S. allies by removing budget constraints that would otherwise encourage pragmatism. Political scientists will appreciate Darnton’s well-aimed jibes at the major schools of international relations theory, and Latin America specialists will welcome his deft applications of cutting-edge theories to a region long underrepresented in political science scholarship.