The Civil War was the greatest transforming event in American culture. Its memories continue to haunt and inspire people, and it is impossible to imagine what the United States would look like today had it never happened. With some 620,000 deaths, more Americans died in the conflict than in all other wars combined until Vietnam. More than 10 percent of the population was directly involved, and almost every American had a close friend or family member who was killed or maimed in the war. The largest expenditure in a few Southern states after the war was payment for prosthetic limbs to its veterans. The war brought a centralized nation-state, a national income tax, conscription, and the emergence of large bureaucratic and regimented organizations in both the public and private sectors.

Slavery was of course the root of the war. But from the nation's founding (when the process of gradual emancipation began in the North) until 1850,...