In 1971 there were fewer than 200,000 inmates serving time in America’s state and federal prisons. During the 1980s and early 1990s, the American public’s fear of rising violent crime—mainly attributable to the explosion of the crack cocaine trade in the 1980s—inspired many politicians to pass laws that imposed harsher sentences on those who engaged in criminal behavior. “Three strikes” laws, which mandate an automatic life sentence for a third felony conviction, and “truth-in-sentencing” laws, which require violent criminals to serve at least 85 percent of their sentences, combined with America’s “War on Drugs” to fuel a prison population increase of unprecedented proportions. As of 1996, there were more than 1.7 million people behind bars in the United States. California alone has more prisoners than France, Great Britain, Germany, Japan, Singapore, and the Netherlands combined.

Since the...