American Prison by Shane Bauer

Shane Bauer is a reporter for Mother Jones who spent two years detained in an Iranian prison.  Interestingly, he can back and not too long afterwards decided to be an undercover prison guard in a private prison.  The short answer is that it was triggering for him.  Go figure.
The story is the key here, though.  The US penal system was unable to house its exploding population by the 1990s. The country couldn’t build prisons fast enough.  And as so often happens, someone looked at a national crisis and saw a business opportunity. Terrell Don Hutto, a former warden of prison complexes in Texas, cofounded the Corrections Corporation of America (since renamed CoreCivic) in 1983, to great economic reward.  More recently CoreCivic and other private prison companies have found another lucrative growth opportunity: running ICE detention facilities.
But outsourcing incarceration to private companies has an inherent problem. The avowed goal of  the US penal system is humane treatment and rehabilitation of prisoners; but housing, educating and caring for people is expensive, and shareholders expect the biggest profits possible.  Suffice it to say that doesn't happen.  This is a must read in an era of our inhumane treatment of asylum seekers.