The World interweaves two stories—of our interactions with nature and with each other. The environment-centered story is about humans distancing themselves from the rest of nature and searching for a relationship that strikes a balance between constructive and destructive exploitation. The culture-centered story is of how human cultures have become mutually influential and yet mutually differentiating. Both stories have been going on for thousands of years. We do not know whether they will end in triumph or disaster.

There is no prospect of covering all of world history in one book. Rather, the fabric of this book is woven from selected strands. Readers will see these at every turn, twisted together into yarn, stretched into stories. Human-focused historical ecology—the environmental theme—will drive readers back, again and again, to the same concepts: sustenance, shelter, disease, energy, technology, art. (The last is a vital category for historians, not only because it is part of our interface with the rest of the world, but also because it forms a record of how we see reality and of how the way we see it changes.) In the global story of human interactions—the cultural theme—we return constantly to the ways people make contact with each another: migration, trade, war, imperialism, pilgrimage, gift exchange, diplomacy, travel—and to their social frameworks: the economic and political arenas, the human groups and groupings, the states and civilizations, the sexes and generations, the classes and clusters of identity.