Final answer:
The Songhai Empire of Western Sudan lasted the longest among the given options, extending its territories east and north and becoming one of the largest empires in African history. Its military success was based on armies of mounted horsemen, and its sources of income included tribute, royal farms, and tariffs on trade.
Step-by-step explanation:
The Songhai Empire of Western Sudan lasted the longest among the options provided. It extended its territories east and north and became one of the largest empires in African history. The Songhai warriors conquered various cities, including Timbuktu and Jenna. Politically, the Songhai Empire was more centralized than the Mali Empire, with local kings or chieftains being replaced by appointed governors. The empire's sources of income included tribute, royal farms, and tariffs on trade, with exports such as gold, ivory, and slaves being in high demand.