When the U.S. military invaded Iraq, it lacked a common understanding of the problems inherent in counterinsurgency campaigns. It had neither studied them, nor developed doctrine and tactics to deal with them. It is fair to say that in 2003, most Army officers knew more about the U.S. Civil War than they did about counterinsurgency.

The U.S. Army / Marine Corps Counterinsurgency Field Manual was written to fill that void. The result of unprecedented collaboration among top U.S. military experts, scholars, and practitioners in the field, the manual espouses an approach to combat...