B. Their geographic locations
Both the Axum Empire and the Swahili city-states thrived as trade empires due to their strategic geographic locations. The Axum Empire was situated near the crossroads of trade routes between Africa, the Middle East, and India, while the Swahili city-states were located along the eastern coast of Africa, facilitating trade with merchants from across the Indian Ocean. These advantageous positions allowed them to engage in and control lucrative trade networks.