Many have emphasized how war and statebuilding often go together, but Morris argues that war also produces institutional, social, and economic change that in the long run makes war less likely. Paraphrasing Tilly, 'war made the state', but the state then made peace rather than war. More controversially, Morris argues that peaceful and prosperous orders historically have only been brought about through war. This book is insightful, with impressive historical scope, and a delight to read. As in his previous work, Morris tries to compare actual data on living conditions and growth rates across periods. However, many of the core claims are not fully persuasive. Historical trends alone do not imply inevitability or clear causation between prior events and subsequent outcomes. Social challenges other than war such as vulnerability induced by geography and disasters have also fostered demands for governance and statebuilding. Prosperity is clearly lower in stateless societies than early empires, but statebuilding need not entail empire, and there is little effort here to systematically compare empires with state formations at lower scales. Morris acknowledges the significant short-term costs of war and how conflicts often produce future conflict rather than definite outcomes and distinguishes between 'productive' and 'unproductive' war. However, the emphasis on progress makes the book focus primarily on the former, and there is less effort to evaluate the rate of the productive to unproductive war or to clarify if the two types of war can distinguished by something beyond their eventual long-term outcomes. Still, this book is an important and provocative addition to the existing body of work on the decline of conflict that deserves a wide readership.