Two powerfully contradictory images dominate historical memory when we think of Native Americans and colonists in early Pennsylvania. To one side is William Penn's legendary treaty with the Lenape at Shackamaxon in 1682, enshrined in Edward Hicks's allegories of the "Peaceable Kingdom." To the other is the Paxton Boys' cold-blooded slaughter of twenty Conestoga men, women, and children in 1763. How relations between Pennsylvanians and their Native neighbors deteriorated, in only 80 years, from the idealism of Shackamaxon to the bloodthirstiness of Conestoga is the central theme of...