What led to the downfall of the ghana, mali and songhai empires? ?

 Downfall of Mali Empire: Weakened by attacks and internal rewbellion. The Mali lost it's hold on the Gold and Salt trade. The Songhai empire was then able to grow in power and take previously held Mali territories.
 Downfall of Songhai Empire: The moroccan armies invaded songhai, which led the fall of songhai empire.
 Downfall of Ghana Empire:In the 11th century, when the Almoravids, a militant confederation of Muslims, began to attack the empire and even conquered it for a time. Though their grip on power did not last long, the chaos they brought to the region destabilized trade, hurting the empire's sources of income.