Lack of interest in trade and conflict with the people of North was the some of the reasons which caused the downfall of Gahana.
Step-by-step explanation:
There were various explanations behind the downfall of Ghana. The King lost his trading sector. Simultaneously dry season was starting to have a long haul impact on the land and its capacity to continue farming. There is an Arab convention that the Almoravid Muslims descended from the North and attacked Ghana.
Another translation is that this Almoravid impact was slow and didn't include any kind of military dominate. In the eleventh and twelfth century Ghana was fully captured by the Sosso ruler Sumanguru.