Final answer:
The trans-Saharan trade routes were the most significant geographic feature impacting the wealth and power of the Mali, Songhai, and Ghana civilizations, as they allowed for the trade of valuable commodities like gold, salt, and slaves.
Step-by-step explanation:
The geographic feature that had the greatest impact on the civilizations of Mali, Songhai, and Ghana was the trans-Saharan trade routes. These routes facilitated the flow of gold, salt, ivory, and slaves, which significantly contributed to the wealth and power of these empires. The introduction of the Arabian camel and the establishment of these trade routes between Morocco and the Niger River allowed for the emergence of larger political entities and increased prosperity.
For instance, Mali's wealth came not only from control over the gold trade but was also enhanced by its access to the agriculturally rich areas around the Niger floodplain. Songhai expanded upon the territories of Mali and Ghana, growing prosperous by maintaining control over these crucial trade routes, which enabled extensive trade of gold and other commodities in West Africa.
Mali's economic success was supported by its diverse economy, which included not just trade but also specialized agriculture and livestock herding in different parts of the empire. Songhai's growth was also bolstered by its military might, allowing it to extend its reach and consolidate power over the territories previously held by Ghana and Mali.