Mass incarceration on a scale almost unexampled in human history is a fundamental fact of our country today—perhaps the fundamental fact, as slavery was the fundamental fact of 1850. In truth, there are more black men in the grip of the criminal-justice system—in prison, on probation, or on parole—than were in slavery then. Over all, there are now more people under “correctional supervision” in America—more than six million—than were in the Gulag Archipelago under Stalin at its height. That city of the confined and the controlled, Lockuptown, is now the second largest in the United States.