International trade and the development of intertwined global markets makes inter-state war less profitable and probable. This is Norman Angell's simple hypothesis, vigorously defended in The Great Illusion and at the root of an enduring controversy, from the time of its initial publication - on the eve of the First World War - to this day. Well documented, logically argued and persuasive, The Great Illusion is a passionate defense of peace, attacking widely held, yet unquestioned assumptions about the gains from war and the costs of conquest.