One important reason was the exchange of products of the forest and of the semi-arid northern grasslands of inner Eurasia, which were controlled by pastoral peoples, for the agricultural products and manufactured goods of the warmer, well-watered lands of outer Eurasia, including the Mediterranean, the Middle East, India, and China. Also important were the construction of classical civilizations and their imperial states during the last five centuries b.c.e.; classical civilizations invaded the territory of pastoral peoples, securing sections of the Silk Roads and providing security for merchants and travelers. The Silk Road had the continued support of later states, including the Byzantine, Abbasid, and Mongol empires, which also benefited from the trade.
There was a continuing demand for hard-to-find luxury
goods among elites across Eurasia.
Contact led to peoples being exposed to
unfamiliar diseases to which they had little
immunity or effective methods of coping. The spread of some particularly virulent epidemic diseases could lead to deaths on a large scale. The worst example of this occurred in the fourteenth century, when the Black Death, identified variously with bubonic plague,
anthrax, or a package of epidemic diseases,
swept away nearly one-third of the population in Europe, China, and the Middle East. In the long run, the exchange of diseases gave Europeans a certain advantage when, after 1500, they confronted the peoples of the Western Hemisphere, who had little natural protection from the diseases of the Eastern Hemisphere.
Direct connections among the civilizations and cultures of the Americas
were less densely woven than in the Afro-Eurasian region. There was no
equivalent in the Western Hemisphere to the long-distance trade of the
Silk, Sea, or Sand Roads of the Eastern Hemisphere.
• The spread of agricultural products was slower and less pronounced
in the Americas than in Eurasia. The north/south orientation of the
Americas required agricultural practices to adapt to various and distinct
climatic and vegetation zones, whereas the east/west orientation of
Eurasia made crop dissemination easier and quicker there.
• The Americas had no equivalent to the spread of distinct cultural
traditions like Buddhism, Christianity, or Islam that ultimately helped to
integrate distant peoples in the Afro-Eurasian web.
• Nevertheless, the Americas did have zones of interaction, as reflected in
the slow spread of cultural elements.
• Commerce did play an important role in regions where contact was possible
—for instance, along the river networks of North America, in the Amazon
basin, and between the islands of the Caribbean. But the most active and
dense networks of communication and exchange lay within, rather than
between, the regions that housed the two great civilizations of the Western
Hemisphere—Mesoamerica and the Andes.