Are Kilwa Malindi Mombasa Sofala all wealthy Muslim city-states along the east coast of Africa. Which industry contributed most to the economy of these city-states?

Kilwa, Malindi, Mombasa, and Sofala were indeed wealthy Muslim city-states along the east coast of Africa, flourishing from the 10th to the 16th centuries. The economy of these city-states was primarily driven by trade, particularly in gold, ivory, and spices, which were in high demand in markets across the Indian ocean. Their strategic coastal locations facilitated extensive maritime trade networks connecting Africa, the Middle East, and Asia.