In this dissertation I explain how military domains—air, land, sea, space, and cyberspace—develop. The military domain, I aver, is a fundamental organizing category employed by states and their militaries to distinguish between suites of technological capabilities (ships vs planes) and ways of warfare (blockades vs strategic bombardment.) I argue that the development of military domains are the consequence of advocates, inspired by technological change, developing and working to realize a new theory of warfare within a military bureaucracy. These advocates argue that the newly enabled domain provides new ways of waging strategic warfare. However, not all attempts to develop a domain for strategic warfare are successful, and I argue that the success of a domain project is the function of three intervening variables: senior leader- ship interest, interservice rivalry, and civilian intervention. Utilizing original archival research, I explain these patterns of development across three case studies: the development of air, space, and cyberspace within the United States military. Through these case studies I demonstrate that the beliefs developed about the relationship between the future of technology and warfare are consequential for the development of military capabilities and the structure of the international security environment. Explaining the contingent process by which military domains develop, I argue, is critical to understanding the future of conflict in an age of rapid technological change.