It seems to be cause and effect. The US incarceration rate increased was stable for most of the 20th century. It was about the same in 1972 as it was in 1930: https://upload.wikimedia.org/wikipedia/commons/thumb/4/48/U..... By 2005 it had increased by a factor of 5.

That trend, however, lagged a similar increase in violent crime. Violent crime increased by a factor of five from 1962 to 1992: http://www.newgeography.com/files/cox-crime-3.png.

The causation seems to run in the direction of more crime leading to more incarceration. Incarceration rates stayed stable in the 1960s and early 1970s. By the time incarceration started ticking up in the early 1970s, violent crime had already increased by 2.5x. By 1980, the incarceration rate was about 40% higher than in 1960. But violent crime had increased by a factor of 4. The increase in incarceration rate didn’t catch up to the increase in violent crime rate until the mid to late 1990s, when violent crime started edging down.

I’m extremely sympathetic to the idea that criminal justice reform is required now that crime rates have gone down dramatically. But we need to grapple with our own history and the nature of our society. We went through a very violent phase from 1960 to 2000. We don’t know why that happened. But it seems pretty clear that our incarceration rate was a lagging response to that phenomenon.

> By the time incarceration started ticking up in the early 1970s

Don't just bury the lede. What changed in the early 70s that would have caused such a thing.

> We don’t know why that happened. But it seems pretty clear that our incarceration rate was a lagging response to that phenomenon.

Yes, we do know what happened. The 70s saw Vietnam Vets coming back from a pointless war with PTSD and heroin addictions. Nixon signed the Comprehensive Drug Abuse Act in 1970. Reagan threw gas on the smouldering fire with the Comprehensive Crime Act and bang, everything is illegal and now with the mandatory minimum sentencing. At every opportunity the federal government, rather than evaluating to see if these laws were effective, chose to make more things criminal. This didn't dissuage gangs from engaging in illegal activity. It actually made them more paranoid and more violent. Anynone that might have been remotely considered a snitch or narc was killed. If you're staring down a life sentence if you got caught might as well remove any doubt.

I didn’t mention the drug war because it doesn’t explain the increase in crime rate—it’s about a decade too late. The increase in violent crime actually began in the 1960s. By the time the DEA was created in 1973, violent crime had more than doubled since 1963. It then actually slowed down a bit—it increased only another 50% from 1973-1983. By the start of Reagan’s term in office, violent crime was already near peak levels. (It would increase about another 1/3 before peaking in the early 1990s.)

Vietnam is one possible explanation, having started in 1955. I have never seen any analysis of that. But unlike the drug war, at least the timing works out.

Is the Baby Boom sufficient explanation? Just having a lot more young adults rattling around, not fully attached and at loose ends tends to spike violence.

I half suspect that long-term declining fertility rates is one reason we currently have such historically low rates of violence.

What happened to the number of police in that same time period? Was there actually an increase in crime or did the amount of it being recorded just increase?

The number of police officers per capita increased by 30% from 1960-1970, but increased only moderately after that, peaking at about 40% above 1960 levels: https://eml.berkeley.edu/~jmccrary/chalfin_mccrary2014b.pdf. Violent crime rate more than doubled from 1970 to 1990 while police per capita went up only 10-20%.

Moreover, the overall increase in violent crime tracked the homicide rate. Homicides are very well reported, throughout the modern era. The homicide rate doubled from 1963 to 1973. That almost certainly reflects an actual increase in homicides, or just previously unreported homicides being reported due to increased policing.

Good thing we got the lead out

A very large part of the prison population across the country comes from people convicted of a felony, given probation, and being kicked off of probation. The number 1 way to get kicked off probation is failing a drug test. The war on drugs led to the massive prison expansion since 1972 in the usa

And conveniently, mostly to the kind of communities like blacks and latinos more likely to use some cheapo drugs, and not to the kind of communities (basically rich white people) using the expensive shit (basically coke, which in the 70s and 80s was everywhere)...