Amid the aristocratic ranks of the Confederate cavalry, Nathan Bedford Forrest was untutored, all but unlettered, and regarded as no more than a guerrilla. His tactic was the headlong charge, mounted with such swiftness and ferocity that General Sherman called him a devil who should be hunted down and killed if it costs 10,000 lives and bankrupts the treasury. And in a war in which officers prided themselves on their decorum, Forrest habitually issued...