Response to King Leopold

I thought it was interesting that Arabic countries were able to have African slaves. The Arab countries were of the poorer countries but Africans were still below them in a sense. It is a shame that Africans were stooped down to the lowest of the low that they could even be owned by people who were perceived to be lower class before African slaves began to be traded. Was it almost a trend or fad to have African slaves now? Who were considered "slaves" before the Africans?