During the campaign and subsequent presidency of Nixon, much of his rhetoric revolved around two things in particular - crime and drugs/drug use. Nixon was the progenitor of the War on Drugs and even coined the term (although Reagan would supercharge it during his time in office).

Nixon's presidency is the time where academics begin to refer to a period defined by 'mass incarceration', where we started to heavily enforce and criminalize drug offences, particularly marijuana. Behind such efforts was forms of racist pandering, often seen as a backlash to the Civil Rights and Black Power movements. We can see this particularly when it comes to drug usage, as the Nixon administration sought to associate African-Americans with drug use in order to excuse the criminalization and policing of their leaders and communities. We see this in particular with the infamous quote from Nixon's top domestic advisor, John Ehrlichman:

*"The Nixon campaign in 1968, and the Nixon White House after that, had two enemies: the antiwar left and black people. You understand what I’m saying? We knew we couldn’t make it illegal to be either against the war or black, but by getting the public to associate the hippies with marijuana and blacks with heroin, and then criminalizing both heavily, we could disrupt those communities. We could arrest their leaders, raid their homes, break up their meetings, and vilify them night after night on the evening news. Did we know we were lying about the drugs? Of course we did.”*¹

Nixon himself wasn't above racial remarks either. In a taped recording, he stated in regards to marijuana legalization supporters: *"You know, it's a funny thing, every one of the bastards that are out for legalizing marijuana are Jewish. What the Christ is the matter with the Jews, Bob? What is the matter with them?"*²

During this time, there was even a commission appointed by Nixon to study the effects of Marijuana (as the Controlled Substances Act was being authored). However, when the commission found the cannabis use did not present a danger to society as the administration often presented, it was ignored.

Fast forwarding to Reagan, and we see the kickstarting of the conservative legal philosophy commonly known today as 'tough-on-crime'. It advocated for harsher criminal penalties for those convicted of a crimes (particularly violent crimes and drug offenses). Mandatory minimum sentences were established, forcing those convicted of a crime to have to serve a specific period of time for that crime (in the Clinton years this would be followed by 'truth in sentencing' laws that made those convicted of a crime have t serve a signficant portion (85%) of their sentence before being eligible for parole). Criminal penalties for drug offenses were increased heavily, particularly with the Drug Abuse Act of '86. This law also introduced penalties for crack cocaine possession, which were far harsher than for powder cocaine (something often regarded as a way to unfairly discriminate against African-American). This particular way of thinking in regards to crime lasted through Bush Sr.'s presidency.

From the period of 1970 to 1994, the prison population increased exponentially - from around 200,000 in 1970 to 1.5 million in 1994. Without a doubt, this trend was guided by the actions that the federal government took during this time in regards to how it handled crime, drug use and dependency, as well as race relations.

Sources or related readings:

1. 'Legalize it All' by Dan Baum, Published in Harper's Magazine April 2016

2. Nixon Oval Office Tape, May 26th, 1971

• The New Jim Crow by Michelle Alexander

• I recommend looking into the Shafer Commission, as well as the earlier LaGuardia Report which was published in 1944 and came to many of the same conclusions as the later Shafer Commission. Both are important in regards to the history of drug prohibition in the U.S., and the LaGuardia Report is important especially in regards to the relationship between prohibition and racial discrimination.

Edit: corrected a typo describing the Shafer commission being appointed by Reagan instead of Nixon

Edit 2: if you have a response or question to my post, please DM me. I'm seeing notifications for responses but they don't appear when I check them.

This previous AH answer by /u/Gorrest-Fump is related.

https://www.reddit.com/r/AskHistorians/comments/71j5qa/has_the_american_prison_system_always_had_a_much/dncua67?utm_source=share&utm_medium=web2x

Which I would paraphrase as "the treatment of black people in the prison system is a direct reaction to the ending of slavery". The missing part is whether this heavy-handed treatment spilled out onto society in general, resulting in high incarceration rates for everyone, not just black people.

So far, the war on drugs is big contributor, explaining the policing used to incarcerate people. What about the privatization of jails, it's often mentioned as contributing the dynamics. when did this happen, how and why?

Would the privatization of jails not have driven the need to keep them at close to full occupancy to justify expenditure on them?

Could an issue be some countries don’t report how many they have in prison? Which would make the US percentage rise even higher?