Book about ancient African tribes

A book in the Schattenjäger library, set between other books on Africa.

Excerpt
Republic of Benin, before slaving devastated the region, it held within its borders some of the most powerful tribes Africa ever produced: the Fons, the Adja, and the terrible Agris.

The tribes of the western region were vicious and xenophobic and almost constantly at war. This part of Africa is called the Red Basin because of the vast amount of bloodshed that occurred there over the centuries.