Sunni Ali's actions in Africa in the mid-1400s had the greatest impact in the demise of what empire?

Sunni had the greatest impact in the demise of the Mali Empire. Ali was the first king of the Songhai Empire, located in Africa and the 15th ruler of the Sunni dynasty. Under Sunni Ali's infantry and cavalry many cities were captured and then fortified, such as Timbuktu (captured in 1468) and Djenné (captured in 1475).

Timbuktu started out as a seasonal settlement and became a permanent settlement early in the 12th century. It became part of the Mali Empire early in the 14th century. In the first half of the 15th century, the Tuareg tribes took control of the city for a short period until the expanding Songhai Empire absorbed the city in 1468.

Djenné also belonged to the Mali Empire.