The reason slavery was able to last so long is that the 13th Amendment has a loophole. (Did you notice it? It went right past me.) The loophole is “except as a punishment for crime whereof the party shall have been duly convicted”. So if you can rig the local laws and get the cooperation of the local law enforcement and court system, you can convict people of “crimes” pretty much whenever you want.
~ Doug Muder, from Slavery Lasted Until Pearl Harbor