The war on drugs is an excuse to criminalize being black, poor, or some other flavor of undesirable. Then the police round you up for drugs and put you in prison. Then the three strikes laws came and if it was the third time they got you, it was a felony and you got even more prison time. Add private prisons into the mix and you get judges being bribed to pipeline people into prison, along with prosecutors and police incentivized in other ways to put people in prison and the result is the American prison system, with a higher percentage of incarceration than any other nation in the world. Yes, including the 'repressive' states like China and Russia.

And to feed the prison industrial complex, of course.