The true statement about how West African economies were impacted by global trade is: "West African trading empires lost power as alternative sources of raw materials became available."
This reflects the historical trend where the rise of European colonial powers and the discovery of new sources of raw materials in different parts of the world diminished the influence and control of established West African trading empires, such as the Ghana, Mali, and Songhai empires. As European powers began to exploit resources from other colonies, the economic power of West African states weakened.