This dissertation examines the institutional processes that led a country founded on a grave distrust of standing armies and centralized power to develop and maintain the most powerful military in history. I theorize that, after World War II, the importance of the defense sector of the economy to defense industries, Department of Defense personnel and key members of Congress created strong incentives to perpetuate and expand the U.S. military industry. Using a multi-method approach–including quantitative methods, mapping techniques, archival research and qualitative analysis–I find that overlapping institutional interests encourage policymakers to extend defense procurement expenditures independent of their national security goals. Analysis of an original database demonstrates that economic and political factors encourage military spending in more rural areas with less diverse economies–areas that are disproportionately reliant on the defense dollars that they receive. The extension of defense benefits to more economically dependent constituencies has coincided with policies that systematically reduce the public costs of war, including deficit financing, a growing use of private contractors, and an all-volunteer military. This gives key constituencies a disproportionate stake in the military economy and makes it easier for policymakers to maintain a defense establishment without fear of electoral reprisal. I argue that, as a consequence, expansive defense resources have allowed the president to act with greater independence from Congress. While the hierarchical structure of the executive branch encourages presidents to initiate military and foreign policy–which historically includes neutrality, diplomacy and military engagements–the administration's capacity to direct military actions without ongoing congressional cooperation depends largely on available resources and institutional authority. As long as congressional budgetary authorizations provide ongoing defense resources available for mobilization at any time, presidents enjoy increased flexibility in directing military engagements independently. Evidence suggests that political power concentrates when separate institutions find shared incentives to cooperate, regardless of institutional mechanisms designed to disperse power. Coinciding interests in defense sector expansion aggregate resources and authority in the executive branch, weakening the system of checks and balances.