The empires of pre-colonial Africa

This is one of the Washington Post's "40 more maps that explain the world."  For now, I'll just leave it here for possible future reference.

"This map of indigenous African empires is not exhaustive. It spans two thousand years from 500 B.C. to 1500 A.D., so these empires were not concurrent; some existed centuries apart. But it shows that... sub-Saharan Africa was rich with vast and powerful empires long before the Europeans arrived... The Songhai Empire, at its peak in the 14th century, was a global center of culture and learning, based in the still-famous mosques of Timbuktu."