America's criminal justice system has, in many ways, become a substitute for the US's largely gutted mental health system. You may have heard something like that before, but never has it been clearer than in this map from MetricMaps:

The map essentially tells two stories: the rise of mass incarceration and the collapse of America's public mental health system.

From the 1970s through the 2000s, America began locking up a lot more people as part of the country's broader shift to tough-on-crime laws to deal with skyrocketing crime.

At the same time, the country pulled back and defunded its public mental health system. This wasn't, at the time, totally malicious — the system during the '60s and '70s was plagued with abuse and neglect, captured in popular media like One Flew Over the Cuckoo's Nest.

The problem is a new public mental health system wasn't built in its place. States, in fact, cut back on mental health spending even more after the Great Recession. That left the criminal justice system as the only system that can respond to people with mental illness in most areas across the country.

The result, as outlined by a 2014 national survey by the Treatment Advocacy Center: "Not only are the numbers of mentally ill in prisons and jails continuing to climb, the severity of inmates' illnesses is on the rise as well." Ultimately, the survey found that the number of people with serious mental illness in prisons and jails outnumber those in state hospitals 10 to 1.

For more on this topic, check out Vox's in-depth explainer.