Not true at all.
The tribes in present day nigeria fought no more than any where else, and were obviously divided because there was no "nigeria". It was not by any degree "war torn".
Yorubal land and the benin empire have never had any kind of whole scale conflict.
The Hausa confederations, joined, seperated and reformed amongst themselves for as long as there have been hausau people. They were quite self contained, is my point.
The entire world was full of slavery. Europe included. Mass slavery was brought to african shores by europeans.