The central question of social evolution is how we can understand the rise of complex societies with extensive cooperation among millions (and more) of people. In less technical terms, what are the origins of civilizations and empires? I couldn’t help but think about this question during my visit to the Cahokia Mounds. Why was the largest-scale society in North America located in southern Illinois? Why did it arise around 1000 CE?
As readers of my books know, my favored explanation for the evolution of social complexity is the theory of cultural group (better, multilevel) selection. Since throughout most of human history competition between societies usually took the form of warfare, we need to look to the patterns of warfare to understand the rise of civilizations.
Take the case of the Sinic (Chinese) civilization. Over the last three thousand years the cradle of the Chinese civilization, the Yellow River Basin, has been unified by one empire after another. There is no other region on Earth that could rival the Yellow River Basin in the intensity of ‘imperiogenesis’ (proportion of time that it found itself within a large empire). In a series of publications (for example, this one) I have argued that the explanation of this remarkable pattern has to do with the very intensive warfare between nomadic pastoralists (Hunnu, Turks, Mongols, etc) and the agrarian Chinese. This is why China was typically unified from the North (and most frequently from the Northwest) – it was the military pressure from the Great Eurasian Steppe that selected for unusually cohesive North Chinese societies, which then would go on to build huge empires by conquering the rest of East Asia.
Steppe frontiers are crucibles of empires; you add a major river and you are practically guaranteed to have an imperiogenesis hotspot. Examples are numerous: the Nile, the Tigris-Euphrates, and the Indus are the usual suspects. But the first empires in sub-Saharan Africa (Ghana, Mali, and Songhai) arose on the Niger River where it flows through the Sahel. This correlation has been long noted. Karl Wittfogel attempted to explain this observation with his theory of ‘hydraulic empires’, based on the control of irrigation by state bureaucracy, but this theory has been empirically disproved. For example, the major river of eastern Europe, the Volga, was the cradle of a number of empires (Bulghar, the Kazan Khanate, and, most notably, Muscovy-Russia), none of which relied on intensive irrigation. Nor did the Chinese along the Yellow River. In other civilizations irrigation was typically a local, rather than an imperial concern. Most likely, the river effect is due to a combination of good environment for intensive agriculture on alluvial soils and the ease of communications (because transporting goods on water was an order of magnitude cheaper than carting them on land).
Whatever the causal factors, let’s go back to the empirical generalization, that there is something special about a major river flowing though a steppe frontier that predisposes such places to engender complex societies. If you were to look within the American landmass north of Mexico for a spot that would fit this description best, where would it be? Incredibly, southern Illinois.
First, the mightiest river in North America is indisputably the Mississippi. Second, as the Mississippi flows South along the boundary of Missouri and Illinois, it leaves the steppe region (known in North America as the Prairie) just North of modern St. Louis/ancient Cahokia. This can be seen on the map of Gross Primary Productivity, where the Prairie is colored in browns and yellows:
or even more clearly on the map of major biomes from the Cahokia Mounds Interpretive Center:
Note also that Cahokia is located in the far northwest corner of the Mississippian Cultural Area:
This is eerily similar to China, which was invariably unified from the North, and most usually from the Northwest. As a result, Chinese capitals were always located on the Northwestern frontier with the steppe, not in the Yangzi River valley, which is much more centrally located and has much more productive agriculture. In the Mississippian culture, similarly, the greatest plant productivity is in the Southeast (see the map of Gross Primary Production above), yet the first and the largest urban center, Cahokia, is located in the Northwest, on the steppe frontier.
So there are several remarkable similarities between the Chinese and Mississippian civilizations. However, I do not want to push the analogy too far. The population of urban Cahokia was perhaps 30,000 people, whereas populations of Chinese capitals, both in Ancient and Medieval times, easily topped one million. The scale of the Cahokian polity was an order (or two) of magnitude less than that of ancient Chinese empires.
A closer Chinese analog of Cahokia is not the later Imperial period, but the Erlitou Culture (early II millennium BCE), which has been tentatively identified with the shadowy Xia Dynasty (which preceded a better known Shang period). Like Cahokia, the Erlitou Culture was also in the same ambiguous position of being either a very complex chiefdom, or an archaic state (recent excavations suggest that it has achieved the statehood). And we know very little about the territorial extent of the Erlitou/Xia state, just as we are unsure about how far the rule of Cahokia extended. Other such ambiguous cultures include Uruk in Mesopotamia (IV millennium BCE), Egypt under the Dynasty 0 (late IV millennium BCE), and the Indus Valley Civilization (III millennium BCE). Archaeologists still argue whether Uruk, or Mohenjo-Daro, were city-states, or capitals of extensive territorial states.
So Cahokia seems similar to the very first urbanized societies of the Old World. Had not the Europeans arrived in the New World around 1500 CE, perhaps the Mississippian culture would also rise again – and fall again, and so on – in a typical sequence of rise and demise that was the historical pattern in Egypt, Mesopotamia, India, and China. However, the urbanized Mississippian culture arose much later than its Old World analogs. Why couldn’t a complex society evolve in North America before c.1000 CE?
I think there are two factors that determined the timing of the rise of the Mississippian civilization. First, it was only during the first millennium of the Common Era that intensive maize agriculture developed in the Mississippian region. As we know well, a productive agrarian base is a necessary condition for large-scale, complex societies. This is the standard explanation that you will see in archaeological books and articles. But intensive agriculture is only a necessary condition, not a sufficient one. Many regions on Earth had agriculture, but did not develop states until they were colonized by European Great Powers.
The second factor, I would argue, was the diffusion of bow-and-arrows into the Mississippian region from the northwest during the second half of the first millennium. The introduction of this novel military technology must have led to more destructive warfare in the Mississippian region, leading to more intense cultural group selection, and then on to larger-scale societies. Perhaps people of the Oneota Culture, who lived in the Prairies to the northwest of Cahokia, were the functional equivalent of the steppe nomads northwest of the Chinese?
Of course, archers on foot in the American Great Plains are a far cry from the mounted archers of the Great Eurasian Steppe. They were probably a much lesser threat to agrarian societies. But the Mississippian polities were also of a much lesser scale than the Chinese empires. It is a reasonable proposition that similar evolutionary mechanisms were operating, but on a much reduced scale in North America, compared to the Old World.