“Jenkins’ rare combination of psychological theorizing and archival research in several countries and time periods yields a fascinating new take on the central question of when states over-estimate or under-estimate others’ resolve. The biases that leaders and elites fall prey to appear to vary with their emotional states and senses of well-being, factors that most scholars have ignored.”—Robert Jervis, author of How Statesmen Think This groundbreaking book explains how the happiness levels of leaders, politicians and diplomats affect their assessments of the resolve of their state’s adversaries and allies. Its innovative methodology includes case studies of the origins of twelve wars with Anglo-American involvement from 1853 to 2003 and the psycholinguistic text mining of the British Hansard and the U.S. Congressional Record.