The first event had been the drying of the Sahara, which had driven new immigrants into West Africa and, from the admixture of these new people with the previous inhabitants, a new vitality developed.
Then, the introduction of the yam and the banana, as previously noted, significantly increased the food supply.

Finally, the developments of iron tools and of iron work further increased the food supply and also provided better weapons.

This permitted increased military power and political expansion.

These were the necessary ingredients that led to the building of three large and powerful empires: Ghana, Mali and Songhay.
Commerce was another factor which contributed to their development.
Governmental control of a thriving trade in both gold and salt provided the wealth and power necessary for establishing these large empires.
Unfortunately, our knowledge about West Africa's early history is severely limited by the lack of written records from that period.

In recent years, archaeologists have been unearthing increasing amounts of material which contribute to our knowledge of early Africa.