The various Caliphates had massive castration centers that would also act as slave markets. Pic related describes how these markets were usually manned by minorities by pointing to the example of the various Andalusian city states. It is important to note that they were used to ethnically clease people other than Black people such as Visigoths. This actually overall had a destablizing effect in the long run and basically left to huge skill gaps because these minority groups tended to have a lot of scientific, philosophical and technical knowledge. It also lead to the problem of people trying to justify new people to enslave which destabilized various places.