In the 1970s, the United States had an incarceration rate comparable to those of other liberal democracies—and that rate had held steady for over 100 years. Yet today, though Americans make up 5 percent of the world’s population, we hold nearly one-quarter of its prisoners. How did we get to this point?

Michelle Alexander and other reformers argue that the failed War on Drugs, draconian sentencing laws, and the private prison complex have driven the now decades-long surge in our prison populations. If only we can fix these problems, the thinking goes, we can bring an end to mass incarceration in America.

But as legal scholar John F. Pfaff reveals in Locked In, this reigning consensus is misguided and will only make it harder to solve the crisis. Pfaff points to overlooked culprits, including a major shift in prosecutor behavior that occurred in the mid-1990s, when prosecutors began bringing felony charges against arrestees about twice as often as they had before. He describes a fractured criminal justice system, in which counties don’t pay to imprison the people they send to state penitentiaries, meaning they have no incentive to send fewer. And he shows that if we hope to significantly reduce prison populations, we have no choice but to think differently about how to deal with people convicted of violent crimes.

A revelatory, clear-eyed investigation into the root causes of mass incarceration, Locked In transforms our understanding of what ails American criminal justice and ultimately forces us to reconsider how we can build a more equitable and humane society.