Looking at US incarceration data over time, the causes are plainly obvious. Mass incarceration began shortly after the civil rights movement was ended, when Nixon launched the War on Drugs in 1971, and then skyrocketed in the 80s as even harsher bipartisan anti drug laws were passed while at the same time the CIA was found to be facilitating the importation of billions of dollars of cocaine into inner cities at the inception point of the crack epidemic.

https://en.m.wikipedia.org/wiki/Incarceration_in_the_United_...