Energy security is a fundamental requirement for national security, and global energy competition threatens to make Department of Defense (DoD) missions increasingly vulnerable to the whims of energy suppliers. DoD’s approach to energy security must accommodate a highly uncertain outlook for energy resource availability. Although U.S. energy security needs are currently met, the shrinking gap between global supply and demand draws the world closer to a point at which competition disrupts social and geopolitical normalizing forces, and conflict becomes likely. While DoD expresses concern over trends that are threatening energy security, Defense planners still operate as if adequate energy supplies will continue to be available without interruption into the extended future. What limited energy-related planning that is currently done addresses only the symptoms of a systemic over-reliance on very few energy resources. This analysis offers key insights into what a shifting energy security environment is, and the paper provides a novel theoretical framework for how the United States can best respond to this ever changing energy security environment.