different regions of Afro-Eurasia through the silk roads. One reason was that,
with few animal domesticates, transportation systems were less developed in
the Americas. Here, humans were the primary beasts of burden.
How similar are the histories of Agrarian civilizations in Afro-Eurasia and
the Americas? The timing of major thresholds is clearly different. In the
Americas similar phenomena appeared, but with a time lag of approximately
3,000 years. For example, we have seen that the city of Monte Alban emerged
late in the 1st millennium B.C.E., almost 3,000 years after the ¿ rst large
cities had appeared in Afro-Eurasia. By 1500 C.E., large imperial structures
had appeared that may be comparable with the political systems of Afro-
Eurasia in the 2nd millennium B.C.E., though they were never as large as
the Achaemenid Empire at its height. Nevertheless, the general trajectory of
change is similar.
In both zones, agriculture appeared independently in several regions and
led to population growth; increasing exchanges; and the evolution of cities,
states, and empires. As a result, within just two to three millennia of their
appearance, Agrarian civilizations incorporated most of the people living in
these two world zones. Agrarian civilizations in both zones shared the same
emergent properties: cities, militarized states, writing systems, monumental
architecture (pyramids seemed to crop up everywhere!), tribute-taking
systems, and extensive networks of exchange. American civilizations also
displayed a Malthusian pattern of rise and fall. As in Afro-Eurasia, there was
plenty of innovation in the Americas, but never enough to avoid eventual
demographic collapses. These similarities suggest that similar drivers
operated in both zones. Collective learning drove innovation, leading
to population increase, which generated a common set of problems and
opportunities that yielded parallel solutions and outcomes. There is indeed a
shape to human history, and the comparison between these regions illustrates
that fundamental truth about human history.
We have seen that, despite many important differences, there were striking
similarities in the histories of the different world zones. These suggest that
in all zones similar forces were at work. Now we start to explore how these
forces shaped the Modern era of human history. Ŷ