Many military analysts now argue that the challenges of Iraq and Afghanistan have prompted a paradigm shift within the U.S. armed forces. They believe that techno-centric formulaic concepts of warfare, such as effects-based operations, have been replaced by more complex, human-centered approaches, such as those laid out in the 2007 Counterinsurgency Manual. This essay details the evolution of U.S. military thought about warfare. It discusses how lessons from the past shaped current policy, the impact of a technologically inspired Revolution in Military Affairs (RMA), and the subsequent conviction that properly equipped U.S. armed forces could rapidly and decisively defeat any and all opponents. The inability of U.S. forces to achieve national objectives in either Iraq or Afghanistan despite their success on the battle1/2eld has caused war intellectuals to seek new lessons from history, question the existence of an RMA, and formulate a new vision of war that stresses uncertainty, adaptation, and innovation. 2011 by the American Academy of Arts & Sciences.