Please summarize the chapter on "How Africa Became Black" from Guns, Germs, and Steel.
This is Chapter 19 of the book. The point of this chapter is to explain why the people who spoke Bantu languages came to dominate sub-Saharan Africa. As he does throughout the book, Diamond attributes this to the advantages conferred by agriculture. Diamond argues that Bantu speakers came to dominate southern Africa because they had agriculture. They were able to out-compete the Khoisan and the Pygmies who were still hunter gatherers. The only places that they failed to dominate in this part of Africa were those in which the land and/or the climate was not suited to the crops they grew.
The basic summary of this chapter, then, is that the Bantus came to dominate sub-Saharan Africa because they had agriculture and other ethnic groups did not.