This dissertation explores connections between occupation, class, and state formation, employing comparative and sociological perspectives previously neglected by historians of this topic in order to locate the officer corps more firmly in its social and cultural context. Officers were socialized in responsibility, gentility, and nationalism, closely connected attitudes which encouraged subordination to civilian political control. The ultimate source of this accountability was employment by the nation-state, which provided security in an increasingly unstable society. Officers responded by stressing order and national sovereignty in their peacekeeping duties in the nation's borderlands. Socialization and self-interest also made Jacksonian-era officers much less bellicose than they had been before 1820, which helped to keep the nation out of war with Britain during crises along the Canadian border, while the officer corps dutifully executed policies many of its members disagreed with or found distasteful, like Indian removal or the occupation of Texas. In the process, conflicts with local settlers and authorities reinforced officers' allegiance to the federal government. Army organization and caste structure were ultimately shaped more by subjective social influences like ideals of gentility and organizational phenomena like bureaucracy and careerism than by the needs of military function per se. This thesis provides a study of officers' mentalite, worldview, and motivation, particularly the nuances and paradoxes of individualism and gentility manifested in their balancing of ambition and security through organizational careers and conflict. These behaviours can help historians understand the changing occupational and cultural construction of elite status and the reconstitution of personal ambition and community obligation in nineteenth-century America. The army officer corps was the first national managerial class in the United States, and its experiences anticipated the broader trends toward translocal functional organization and specialization in transferal functional organization and specialization in American society and culture after mid-century. This thesis also examines the construction of military expertise in social, cultural, and institutional context, questioning its content and objectives in new ways, and suggests that American military expertise was primarily administrative and logistical rather than tactical or strategic. This bureaucratic expertise reflected a successful adjustment to the problems of scale, scope, and complexity encountered by the nation's largest organization, reinforcing the army's sense of political accountability and preparing it to effectively manage the mass armies of the Civil War. As a whole, this dissertation demonstrates the social construction of military professionalism and the decisive role of the state therein, providing a paradigm of bureaucratization, social and institutional consolidation, and class and state formation in nineteenth-century America.