The document provides an overview of several West African kingdoms including Ghana, Mali, and Songhai. The kings of Ghana became wealthy by taxing salt and gold and controlling the price of gold. Under Mansa Musa, Mali grew extremely wealthy from the gold-salt trade and brought attention to the empire when Musa took his pilgrimage to Mecca. Askia Muhammad strengthened Songhai's government and resumed trans-Saharan trade after his own pilgrimage, making Timbuktu a center of culture and learning once again.