The factor that contributed to the rise of African empires such as Ghana and Mali is: "A, their creation and involvement in trade networks"
The beginnings of Ghana in the 400s include a group of nomadic people which name were Berbers that founded a kingdom at the south of the Sahara desert and named it Ghana. There, they started to carry goods across the Sahara desert on camels. The empire of Ghana began thanks to the Soninke (A group that controlled Ghana) that built their capital city on the edge of the Sahara and in a little time, the city became the most important southern trade center of the Saharan trade routes. Eventually Ghana started to grow rich thanks to the trans Saharan trade.
The beginnings of Mali, located in the west Africa, the Sahel. Mali got power by controlling the big and rich trans Saharan trade routes. Mali had a good location in an agriculturally rich area that gave it the possibility to control the gold trade of the Niger River and to have this in control, was what helped Mali to grow as an empire.