Common law, jury and trial (I think)
Passed by Congress on January 31, 1865, and ratified on December 6, 1865, the 13th amendment abolished slavery in the United States and provides that "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.
Most Southerners believed they were naturally better than African Americans and therefore had the right to "own" them, while many Northerners thought it was morally wrong, but some Northerners didn't want the competition of enslaved labor.