This is a study of two topics of central importance in late medieval history: the impact of war, and the control of disorder. Making war and making law were the twin goals of the state, and the author examines the effect of the evolution of royal government in England and France. Ranging broadly between 1000 and 1400, he focuses principally on the period c.1290 to c.1360, and compares developments in the two countries in four related areas: the economic and political costs of war; the development of royal justice; the crown's attempt to control private violence; and the relationship between public opinion and government action. He argues that as France suffered near breakdown under repeated English invasions, the authority of the crown became more acceptable to the internal warring factions; whereas the English monarchy, unable to meet the expectations for internal order which arose partly from its own ambitious claims to be 'keeper of the peace', had to devolve much of its judicial powers. In these linked problems of war, justice, and public order may lie the origins of English 'constitutionalism' and French 'absolutism'.