Many of the ‘lost’ cities mentioned were in existence thousands of years before mussulman existed, or Christianity, for that matter. Chattel slavery came much later with the coming of Islam.
Article claims first great African city was started 900 BC. That’s 1,500 years before Mohammad was born, not “thousands.”
Article does point out the first native African city was built thousands of years after the great Nile River Valley Civilization.
It is perplexing. How could the Egyptians create such civilization starting around 3,100 BC and just a couple thousand miles south on the same continent...NOTHING. The Africans didn’t travel north and the Egyptians only went hundreds of miles south to mine stone for buildings.