The book is also galvanizing white readers, including some who might question its portrayal of the war on drugs as a continuation of race war by other means.

“The book is helping white folks who otherwise would have simply dismissed that idea understand why so many people believe it,” said David M. Kennedy, director of the Center for Crime Prevention and Control at the John Jay College of Criminal Justice. “It is making them take that seriously.”

“The New Jim Crow” arrives at a receptive moment, when declining crime rates and exploding prison budgets have made conservatives and liberals alike more ready to question the wisdom of keeping nearly 1 in 100 Americans behind bars. But Professor Alexander, who teaches at the Moritz College of Law at Ohio State University, said in an interview that the more provocative claims of her book did not come easily to her. When she first encountered the “New Jim Crow” metaphor on a protest sign in Oakland, Calif., a decade ago, she was a civil rights lawyer with an impeccable résumé — Stanford Law School, a Supreme Court clerkship — and was leery of embracing arguments that might be considered, as she put it, “crazy.”

Professor Alexander, who is black, knew that African-Americans were overrepresented in prison, though she resisted the idea that this was anything more than unequal implementation of colorblind laws. But her work as director of the American Civil Liberties Union’s Racial Justice Project in Northern California, she said, opened her eyes to the extent of the lifelong exclusion many offenders face, including job discrimination, elimination from juries and voter rolls, and even disqualification from food stamps, public housing and student loans.

“It’s easy to be completely unaware that this vast new system of racial and social control has emerged,” she said. “Unlike in Jim Crow days, there were no ‘Whites Only’ signs. This system is out of sight, out of mind.”

In conversation, she disputes any suggestion that she is describing a conspiracy. While the title is “provocative,” she said, the book contains no descriptions of people gathering secretly in rooms.