Conventional wisdom of the moment tells us that the great war of 1861—1865 was “about” slavery or was “caused by” slavery. I submit that this is not a historical judgment but a political slogan. What a war is about has many answers according to the varied perspectives of different participants and of those who come after. To limit so vast an event as that war to one cause is to show contempt for the complexities of history as a quest for the understanding of human action. Two generations ago, most perceptive historians, much more learned than the current crop, said...