African rulers found European goods sufficiently desirable to hand over captives which they had taken in warfare. Soon, war began to be fought between one community and another for the sole purpose of getting prisoners for sale to Europeans, and even inside a given community a ruler might be tempted to exploit his own subjects and capture them for sale. A chain reaction was started by European demand for slaves (and only slaves) and by their offer of consumer goods—this process being connected with divisions within African society.

p. 119. - How Europe Underdeveloped Africa (1972)