In the 1930s, the fictional Lone Ranger -- a Texas Ranger who had survived an ambush by outlaws and was nursed back to health by his faithful companion Tonto -- made his first appearance as the "Masked Rider of the Plains," come to rescue people in trouble. Perito, in this groundbreaking and extremely timely study, invokes him to remind readers that there is nothing in American history that makes the recent disinterest in constabulary missions inevitable. In fact, many contemporary situations, most under the broad heading of "peacekeeping," demand just such constabulary forces to combine police work and military duties. Iraq has served as a stark reminder of the consequence of the U.S. failure to develop specialized units for postconflict security. Perito provides valuable analysis, drawn from firsthand experience, of the role of such units in the Balkans in the 1990s -- and shows how little Washington learned from this experience. Its aversion to constabulary forces persisted even as it embarked on nation-building in Afghanistan and Iraq.