What are the motifs in Salt: A World History by Mark Kurlansky?

An important motif, in many ways related to the idea of alternative history is the importance of the search for resources in human history. It is the importance of the "search" for resources rather than just the resources themselves that are important because it the act of searching for these resources that motivates men and women to develop new processes, found new cities, start new trading patterns that, in turn, have tremendous unintended consequences on the lives of people around them.