This book is based on the Wiles lectures for 1981 delivered at the Queen's University of Belfast in October 1981. It is not a history of Anglo-American relations in the century; its theme deals with how the United States of America came to replace Britain as the primary world and oceanic power confronting a grouping of land-based continental powers, the position Britain occupied throughout the nineteenth century. This theme is examined in the light of how the process of replacement was conceived and perceived by those groups which had the primary responsibility for the formulation and conduct of foreign relations in each of the two powers, Britain and America. The author, whose earlier study of 1965 of the British foreign-policy-making elites pioneered this approach in Britain, argues the existence and continuity over much of this century of similar groups in the United States.