The Bronze Age was, however, unique even in ancient times in that the great river valley civilizations relied on metal for production and that metal (copper, tin, lead, etc.) was scarce and had to be procured from afar, from less developed regions. Thus trade involved not just luxuries but also basic requirements, interaction between societies at contrasting levels of technology and social organization, and organization by ruling elites … Bronze Age societies [however] were not inchoate versions of our own.

Over against the processes of divergent development leading to the separation of distinct peoples – and confusion – can be traced no less clearly a process of convergence…. At least in the Old World the peoples accessible to archaeological study were constantly interchanging material objects, ideas and inventions…. What we call Civilization is the product of this collective tradition, transcending all national frontiers.