[jki275]

Slavery is not allowed in the US Constitution. The 13th Amendment specifically abolishes it.

https://www.archives.gov/milestone-documents/13th-amendment

[hjanssen]

With a specific exception: "(...) except as a punishment for crime whereof the party shall have been duly convicted".

So it does still exist - but America only considers criminals for it. From what I've gathered, though, that is still a lot of people.

[iso1631]

Your link specifically allows it