Final answer:
The ancient western African kingdoms of Ghana, Mali, and Songhai all established economies based on trade, flourishing through their strategic location along important trans-Saharan trade routes and control of valuable commodities such as gold and salt. The correct option is d.
Step-by-step explanation:
The ancient western African kingdoms of Ghana, Mali, and Songhai had several commonalities, but in response to the question, the correct answer is that these kingdoms established economies based on trade. All three empires were strategically located to take advantage of trade routes that connected different parts of Africa with the Mediterranean world, Europe, the Near East, southwest Asia, and beyond.
The ancient Ghana Empire excelled through its control over the trans-Saharan gold and salt trade, while the Mali Empire, following in Ghana's footsteps, continued to prosper through trade, significantly in gold, and eventually converted to Islam, which further influenced its trade networks. The Songhai Empire also depended heavily on controlling trade routes for its prosperity, particularly under the rule of the Soninke-speaking people. Thus, trade was a fundamental element of each empire's economy and was vital to their success.