The prevention of war in the 20th century is examined in an attempt to analyze the way in which it is discussed and the ideologies involved. Using examples from modern history, the book sets out to remedy what the author describes as an astonishing deficiency in popular political or international relations theory. The book argues that the basis of debate is largely ideological and that modern thinking about peace and war is best understood as a contrast between five major ideologies - militarism, crusading, defencism, pacific-ism (the thinking of those members of the peace movement who do not reject all war) and pacifism. It is suggested that the outcome of the contest is affected not only by the objective facts of the international climate but also by the historical factors of political climate and strategic situation. Martin Ceadel is the author of Pacifism in Britain 1914 - 1915: the Defining of a Faith and is currently working on a history of the British peace movement.