I often bring this fact out to Black Muslims who renounced the white man's religion i.e. Christianity. It is a very hard for them to believe that their newly enmbraced religion was the very religion that brought this evil upon their ancestors and to this day is still practiced in Muslim parts of the world.
Actually slavery goes much further back. The Romans practiced it and probably so did many European peoples (Celtic, Germanic tribes etc). I had not realised the extent of the Islamic role in this evil though.