I wouldn't overlook the money angle either. Privatization, either outright, or in part via service fees for phones, books, commissary, etc, has changed the system.
Slave labor continued - the 14th amendment clearly spells it out : "Neither slavery nor involuntary servitude, except as a punishment for crime whereof the party shall have been duly convicted, shall exist within the United States[...]"
"Companies own or manage 75% of U.S. detention facilities. Two of the biggest companies, CoreCivic and The GEO Group, are publicly traded. In the correctional system, however, less than 10% of state and federal inmates are in the care of private prisons."
