What Caused the Crime Decline? a report by Oliver Roeder, Lauren-Brooke Eisen, and Julia Bowling, with a foreword by Joseph E. Stiglitz and an executive summary by Inimai Chettiar Brennan Center for Justice, NYU Law School, 134 pp., available at www.brennancenter.org

For too long, too many judges have been too quiet about an evil of which we are a part: the mass incarceration of people in the United States today. It is time that more of us spoke out.

The basic facts are not in dispute. More than 2.2 million people are currently incarcerated in US jails and prisons, a 500 percent increase over the past forty years. Although the United States accounts for about 5 percent of the world’s population, it houses nearly 25 percent of the world’s prison population. The per capita incarceration rate in the US is about one and a half times that of second-place Rwanda and third-place Russia, and more than six times the rate of neighboring Canada. Another 4.75 million Americans are subject to the state supervision imposed by probation or parole.

Most of the increase in imprisonment has been for nonviolent offenses, such as drug possession. And even though crime rates in the United States have declined consistently for twenty-four years, the number of incarcerated persons has continued to rise over most of that period, both because more people are being sent to prison for offenses that once were punished with other measures and because the sentences are longer. For example, even though the number of violent crimes has steadily decreased over the past two decades, the number of prisoners serving life sentences has steadily increased, so that one in nine persons in prison is now serving a life sentence.

And whom are we locking up? Mostly young men of color. Over 840,000, or nearly 40 percent, of the 2.2 million US prisoners are African-American males. Put another way, about one in nine African-American males between the ages of twenty and thirty-four is now in prison, and if current rates hold, one third of all black men will be imprisoned at some point in their lifetimes. Approximately 440,000, or 20 percent, of the 2.2 million US prisoners are Hispanic males.

This mass incarceration—which also includes about 800,000 white and Asian males, as well as over 100,000 women (most of whom committed nonviolent offenses)—is the product of statutes that were enacted, beginning in the 1970s, with the twin purposes of lowering crime rates in general and deterring the drug trade in particular. These laws imposed mandatory minimum terms of imprisonment on many first offenders. They propounded sentencing guidelines that initially mandated,…