Answer:
The 13th amendment.
Step-by-step explanation:
The 13th amednment outlawed slavery within the United States. The only exception was that slavery could be used as a form of punishment for someone who was convicted of a crime. This type of loophole will allow for the beginning of what is now known as convict leasing. Convict leasing allowed prisons to rent out people to different companies in order to complete hard labor.
This system was used in the US after the Civil War.