Why are so many Americans behind bars? It's complicated.

The Conversation Chart by Jeffrey Bellin, from CC-BY-ND data

In a country known as "the land of the free," it's hard to reconcile how so many people end up behind bars. "The U.S. continues to imprison a higher percentage of its population than almost every other country. The U.S. incarcerates 530 people for every 100,000 in its population, making it one of the world's biggest jailers," reports Jeffrey Bellin for The Conversation, a platform for journalism by academics.

"As a former prosecutor and a researcher who studies the criminal justice system, I have found that understanding how the U.S. incarceration rate grew over the last few decades is the key to understanding its root causes," Bellin explains. "I think the public debate can improve if people develop a better understanding of how mass incarceration arose and its tenuous connection to crime."

Incarceration rates intertwine with spikes in serious crimes such as homicides and longer sentences, Bellin notes. "Over time, this led to today's aging prison population and many people being held long past the time they would have been released at other times in this country's history. . . . The number of people incarcerated in state prisons for homicide increased by over 300% between 1980 and 2010. . . . But the scale of the increases for other offenses, like drug crimes, is even larger – rising 1,147% over this time frame.

"Substantially reducing prison and jail populations will require a better understanding of the link between incarceration and crime. It is not simply the case that incarceration goes up because people commit crime; instead, the story is much more complicated," Bellin explains. "That is because we use incarceration for two purposes: to obtain justice on behalf of victims and to try to change people's behavior."

Bellin points out two types of cases in the nation's criminal courts. The first type involves violent crimes such as murder or sexual assault. The second type "are cases like drug offenses and weapons possession, which are not typically about obtaining justice for victims but are supposed to further policy goals like preventing drug use." Over the last several decades, courts have increased sentence years and the number of actions that can lead to prison time. The result is massive incarceration.

Is there a solution? Bellin writes, "Substantial progress at reducing the incarcerated population will require reversing both trends. First, returning sentence lengths for all offenses, including serious violent crimes, to their historical norms. And second, resisting this country's growing habit of relying on incarceration as a tool for achieving policy goals."