The correct answer to this open question is the following.
Although there are no options attached we can say the following.
The biggest influence on the development of the West African kingdoms was trade.
Yes, trade was the most important factor in the development of Western African kingdoms because these territories had rich resources of raw materials such as salt and gold that had great value at that time. During this period, West African kings taxed all trade caravans crossing their territories and that represented a good source of income to the kingdoms' arcs. Another important factor in those years was that Islam spread in various regions by Arab merchants.
West African empires utilized centralized governments ruled by kings.
When we are talking about powerful empires in West Africa, the first one that comes to mind is the Ghana Empire that ruled vast territories of what today is modern Senegal, and parts of Mauritania, and Mali. Its power was mostly based on trade. They had gold and traded with other nations. This great Empire ruled the territory from the 8th to 9th century CE.