Since the attacks of September 11, 2001, the United States has developed a national security strategy designed to eliminate the conditions that spawn asymmetric threats. An important part of that is helping build stable, legitimate governments in nations which allowed or supported terrorism and other forms of asymmetric aggression. This has led the United States to renewed involvement in counterinsurgency. The United States, particularly the Army, has a long history of counterinsurgency support. During the past decade, though, this has not been an area of focus for the American military. To renew its capability at counterinsurgency, the military is assessing 21st century insurgency, particularly in Iraq and Afghanistan, and revising its strategy, operational concepts, organization, and doctrine. This monograph is designed to contribute to this process.