In counterinsurgencies, what causes insurgent violence to decline? Through an in-depth examination of US Marine Corps units operating over time in Ramadi, Iraq (Operation Iraqi Freedom) and Garmsir, Afghanistan (Operation Enduring Freedom), this dissertation argues that a particular approach to waging counterinsurgency at the tactical level, referred to here as a dynamic force disposition, is responsible for causing a downward trend in insurgent violence. Such an explanation overrides common accounts of downward trends in insurgent violence in Iraq and Afghanistan, such as the Awakening and the surge.