Final answer:
The Western African kingdoms, particularly Ghana and Mali, maintained control and wealth from the salt and gold trades by taxing all trade that went through their regions, rather than relying on slave labor, tributes, or conquest alone.
Step-by-step explanation:
The kingdoms of Western Africa maintained control over the wealth brought through the salt and gold trades by taxing all trade that came in and out of the region. These medieval African kingdoms, such as Ghana and Mali, controlled resources like gold and salt by establishing a system of taxation on these commodities, which effectively permitted them to accrue wealth and exert influence over trade routes and mining operations. Kingdoms like Mali allowed gold-producing areas to remain quasi-independent vassal states while collecting taxes on trade transactions. They did not rely solely on slave labor, tributes from wealthy families, or complete conquest of neighboring civilizations but rather governed trade routes and relied on warfare and alliances to maintain and extend power.