Peace, many would agree, is a goal that democratic nations should strive to achieve. But is democracy, in fact, dependent on war to survive? Considering this question, two of our most celebrated political scientists trace the shocking ways in which governments have mobilized armies since antiquity, discovering that our modern form of democracy not only evolved in a brutally competitive environment but also was quickly excised when the powerful and elite no longer needed their citizenry to defend against existential threats. Bringing to vivid life many of the major battles that shaped our world today, the authors show how centralized monarchies replaced feudalism, why dictatorships can mobilize large forces but often fail at long-term military campaigns, and how drone warfare has already weakened American democracy. In the spirit of Francis Fukuyama and Niall Ferguson, this book promises to have far-reaching implications and become the centerpiece of debate for years to come.