Parrington and others largely interjected their reflections on states' rights en passant, and their work does not gainsay McDonald's claim that no one has attempted a comprehensive history of the subject. McDonald brings exceptional credentials to this task, for he ranks among the most learned and incisive of American historians, as readily at home with constitutional history and theory as with intellectual, political, and economic history. In particular he brings his considerable acumen to bear on knotty problems that may seem abstract but have grave and direct political consequences. The nature of "sovereignty" and the possibility and desirability of dividing it has absorbed political theorists since ancient times and especially absorbed the Founding Fathers, who made a Herculean effort to establish a republic of an unprecedented kind over a territory vast enough to constitute an empire. McDonald works through the theoretical formulations and attendant practical consequences with a sure hand. No small bonus: he writes well and has a gift for explaining complex theories in plain and often spirited English that readers without a Ph.D. can follow easily.