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The chapter you want to look a is chapter four, which explains how vital the domestication of animals was to certain societies. The domestication provided such groups of people with meat, milk, fertiliser, transport, leather, a military advantage, wool and the means of ploughing fields. In addition the domestication of animals exposed societies to a variety of germs that ended up being crucial in the conquest of other peoples, as the decimation of the New World by smallpox amply demonstrates.
In the concluding paragraph of this chapter, the author points out why the domestication of animals was such a crucial ingredient in explaining why some societies were able to ultimately dominate others:
The resulting food surpluses, and (in some areas) the animal-based means of transporting those surpluses, were a prerequisite for the development of settled, politically centralised, socially stratified, economiclaly complex, technologically innovative societies.
The domestication of animals is therefore one of the key factors that helps explain the question that the book sets out to answer.