@LiberalLibrarian

I got my proof of it being about slavery is right out of the CSA Constitution:

Slavery is addressed 10 times in their "Constitution"

1 example = "No bill of attainder, ex post facto law, or law denying or impairing the right of property in negro slaves shall be passed."

https://avalon.law.yale.edu/19th_century/csa_csa.asp