This is interesting. I never even thought about whether black slaves were owned by black people during the civil ware era, and they were! Approximately 3,400 black owners owned approximately 13,000 black slaves, and did so for the same reason the white owners did... to line their pockets with profits. Some even owned white indentured servants (not clear on what the difference is).
https://www.theroot.com/did-black-people-own-slaves-1790895436
https://www.theroot.com/did-black-people-own-slaves-1790895436