This book surveys US achievements and failures in the world across the 20th century. The analysis builds upon surveys of experts at the Woodrow Wilson International Center for Scholars and several universities conducted over the last 25 years. The reasons for success and failure are subject to hot dispute. Walter Clemens argues that the individual traits of US leaders account for far more variation in outcomes than the domestic or international contexts. He concludes that the policy outcomes of the past century confirm the assumptions of mutual gain theory, complexity theory, and liberal peace theory. Clemens then uses his analysis to sketch alternative futures that could face planners in the early 21st century.