Why did early african trading empires rise and fall

The all three kingdoms in Africa had some difficult times, there are some reasons for the rise and fall, they were based on leadership and economic issues. Ghana rose as a result of good economy and fell as a result of losing monopoly on profitable trade routes. Mali rose as a result of strong military leadership and fell when the empire became too large for a weak king to rule. History repeated itself when the same happened to Songhai.