These quite-different patterns of development within particular civilizations have made it difficult to devise a single, all-encompassing definition of the third-wave era. In one way, however, a common theme emerges, for during this time, the world’s various regions, cultures, and peoples interacted with one another far more extensively. More than before, change in human societies was the product of contact with strangers, or at least with their ideas, armies, goods, or diseases. In a variety of places—Island Southeast Asia, coastal East Africa, Central Asian cities, parts of Western Europe, the Islamic Middle East, and the Inca Empire—local cosmopolitan regions emerged in which trade, migration, or empire had brought peoples of different cultures together in a restricted space. These “mini-globalizations,” both larger and more common than before, became a distinctive feature of third-wave civilizations.

None of these civilizations were wholly isolated or separate from their neighbors, although the range and intensity of cross-cultural interaction certainly varied over time. In limited ways, this had been true for earlier civilizations as well. But the scale and pace of such interaction accelerated considerably between 500 and 1500. Much of Part Three highlights these intersections and spells out their many and varied consequences.

One pattern of interaction lay in long-distance trade, which grew considerably during the third-wave millennium—along the Silk Roads of Eurasia, within the Indian Ocean basin, across the Sahara, and along the Mississippi and other rivers. Everywhere it acted as an agent of change for all its participants. In places where such commerce was practiced extensively, it required that more people devote their energies to producing for a distant market rather than for the consumption of their own communities. Those who controlled this kind of trade often became extremely wealthy, exciting envy or outrage among those less fortunate. Many societies learned about new products via these trade routes. Europe’s knowledge of pepper and other spices, for example, derived from Roman seaborne trade with India beginning in the first century C.E. Such exchange among distant lands also had political consequences, as many new states or empires were constructed on the basis of resources derived from long-distance commerce. Furthermore, religious ideas, technologies, and diseases also made their ways along these paths of commerce, disrupting older ways of living and offering new opportunities as well.

Yet another mechanism of cross-cultural interaction lay in large empires. Not only did they incorporate many distinct cultures within a single political system, but their size and stability also provided the security that encouraged travelers and traders to journey long distances from their homelands. Empires, of course, were nothing new in world history, but many of those associated with third-wave civilizations were distinctive. In the first place, they were larger. The Arab Empire, which accompanied the initial spread of Islam, stretched from Spain to India. Even more extensive was the Mongol Empire of the thirteenth and fourteenth centuries. In the Western Hemisphere, the Inca Empire encompassed dozens of distinct peoples in a huge state that ran some 2,500 miles along the spine of the Andes Mountains.

Furthermore, the largest of these empires were the creation of nomadic or pastoral peoples. Earlier empires in the Mediterranean basin, China, India, and Persia had been the work of settled farming societies. But now, in the thousand years between 500 and 1500, peoples with a recent history of a nomadic or herding way of life entered the stage of world history as empire builders—Arabs, Berbers, Turks, Mongols, Aztecs—ruling over agricultural peoples and established civilizations.

Together, large-scale empires and long-distance trade facilitated the spread of ideas, technologies, food crops, and germs far beyond their points of origin. Buddhism spread from India to much of Asia; Christianity encompassed Europe and took root in distant Russia, even as it contracted in the Middle East and North Africa. Hinduism attracted followers in Southeast Asia; and more than any other religion, Islam became an Afro-Eurasian phenomenon with an enormous reach. Beyond the connections born of commerce and conquest, those of culture and religion generated lasting ties among many peoples of the Eastern Hemisphere.

Technologies, too, were diffused widely. Until the sixth century C.E., China maintained a monopoly on the manufacture of raw silk. Then this technology spread beyond East Asia, allowing the development of a silk industry in the eastern Mediterranean and later in Italy. India too contributed much to the larger world—many food crops, crystallized sugar, a system of numerals and the concept of zero, and techniques for making cotton textiles. In the Americas, corn gradually diffused from Mesoamerica, where it was initially domesticated, to North America, where it stimulated population growth and the development of more complex societies. Disease also linked distant communities. The plague, or Black Death, decimated many parts of Eurasia and North Africa as it made its deadly way from east to west in the fourteenth century.

A focus on these accelerating connections across cultural boundaries puts the historical spotlight on merchants, travelers, missionaries, migrants, soldiers, and administrators—people who traveled abroad rather than those who stayed at home. This cross-cultural emphasis in world history raises provocative questions about what happens when cultures interact or when strangers meet. How did external stimuli operate to produce change within particular societies? How did individuals or societies decide what to accept and what to reject when confronted with new ideas or practices? In what ways did they alter foreign customs or traditions to better meet their own needs and correspond to their own values?

Much of the readily visible “action” in third-wave civilizations, as in all earlier civilizations, featured male actors. The vast majority of rulers, traders, soldiers, religious officials, and long-distance travelers were men, as were most heads of households and families. The building of states and empires, so prominent in the third-wave era, meant war and conquest, fostering distinctly masculine warrior values and reinforcing the dominant position of men. Much of what follows in Part Three is, frankly, men’s history.

But it is useful to remember that behind all of this lay a vast realm of women’s activity, long invisible to historians or simply assumed. Women sustained the family life that was the foundation of all human community; they were the repositories of language, religious ritual, group knowledge, and local history; their labor generated many of the products that entered long-distance trade routes as well as those that fed and clothed their communities. The changing roles and relationships of men and women and their understandings of gender also figure in the chapters that follow.