The role of ecosettlement systems in human social evolution
University of California, Riverside
Abstract: This essay examines the evolution of human institutions by focusing on the ways that people have arranged themselves in space and the uses that they have made of the natural and built environment. Ecosettlement systems are the patterned ways in which humans distribute themselves across the land, the ways in which the inhabitants of settlements interact with people in other settlements and their interactions with nature. Not only have ecosettlement systems evolved along with the rise of social complexity and hierarchy, but they have also played a generative role in human social evolution at several crucial junctures. This paper examines the settlement systems of paleolithic and archaic nomads, the emergence of sedentism, and the co-evolution of sedentary and nomadic peoples. Also considered are the emergence of settlement size hierarchies and the relationship between these and socio-political hierarchies, the emergence and spread of large cities, as well as the patterns of city growth and decline, the emergence of city-states that specialized in trade, the expansion of market exchange and the rise of tributary empires with their capital cities. Also discussed are the emergence of world cities and global cities, and the phenomenon of urbanized regions and megacities in the contemporary global settlement system.
A paper to be presented at the session on “A compound vision: world history seen through many lenses” (organized by David Wilkinson) at the annual meeting of the International Studies Association, Honolulu, Hawaii, Friday, March 4, 10:30am-12:15. Draft v. 3-29-05. (13596 words) The IROWS Empire/City project home page is at http://irows.ucr.edu/research/citemp/citemp.html This paper is available at
Human settlement systems are usually understood to include the systemic (regularized) ways in which settlements (hamlets, villages, towns, cities) are linked with one another by trade and other kinds of human interaction. This essay will indeed study settlement systems understood in this way, but it will expand the notion of settlement systems to include interactions with the environment, and all the patterned ways in which humans use the landscape of the Earth. This allows us to consider the settlement systems of nomads, who often moved across the land in patterned annual cycles, and to examine the “metabolism of settlements” – the flows of energy, water, air, food, and raw materials by which human settlements have been linked with the biosphere and the geosphere. So the notion of settlement systems proposed here includes all the patterned ways in which humans interact with the landscape and with the biosphere and the atmosphere – ecosettlement systems.
It will not be presumed that settlement systems are contained within separate societies. On the contrary, it is usually impossible to understand the systemic patterns of interaction and the division of labor among settlements without looking at settlement systems within whole world-systems – systems of societies. So the unit of analysis in this essay will be world-systems. The relationship between settlements and polities is a fundamental aspect of all social systems. The territorial boundaries of polities are rarely coterminous with the interaction networks in which settlements are embedded, and so settlement systems must be studied “internationally” in all social systems. This lens is used to examine the evolution of human institutions since the time of the paleolithic big game hunters. This is a window on world history and prehistory that allows us to see the big patterns and to discern the systemic logics by which we have evolved from living in nomadic hunter-gatherer bands to living in globalized megacity regions.
Settlements are rarely ever intelligible without knowing their relations with the rural and nomadic populations that interact with them. Archaeologists and ethnographers map out the ways in which human habitations are spread across space, and this is a fundamental window on the lives of the people in all social systems. The spatial aspect of population density is perhaps the most fundamental variable for understanding the constraints and possibilities of human social organization.
Theories of Social Change
One could simply describe the ways in which settlement systems have changed along with the structure of social systems using the tools that urban geographers and anthropologists have devised – settlement size hierarchies, the spatial structure of settlements, etc. Indeed, this is an important task in its own right, and we are far from having accurate and complete data for knowing the timing, growth rates and population sizes of settlements. But there are also important theoretical issues at stake in the explanation of the observed patterns of social change. Are ecosettlement systems only passive outcomes of social change that are mainly determined by other factors, or are ecosettlement systems themselves sources of generative processes that cause the emergence of complexity and hierarchy? What has been the role of settlements with regard to changes in the basic logic of social reproduction? This essay will examine how the role of settlements has changed depending on the nature of the world-systems in which they are embedded.
Some theories of innovation claim that the discovery and implementation of new cultural, organizational and productive technologies are systematically related to settlement systems and their interaction networks. The recent influential book by world historians John R. McNeill and William H. McNeill (2003), The Human Web, employs what can be called a cybernetic perspective to explain innovation – new stuff emerges at important nodes in communications and transportation networks. This is a perspective that was also developed by Amos Hawley (1971), who contended that innovation occurred at major communications network nodes (in cities) where different kinds of information crossed paths, enabling the recombination of elements to produce new ideas and institutions. David Christian’s (2004) excellent Maps of Time employs a similar notion of hubs that are the loci of innovations.
A somewhat different explanation that is also tightly connected to settlement systems is the notion of semiperipheral development proposed by Chase-Dunn and Hall (1997) as a key component of their theory of world-systems evolution. One problem with the cybernetic approach is that it does not explain uneven development, the movement of the cutting edge of innovation. Why does not the initial hub remain remain the center forever? What causes old hubs to decline and new hubs to emerge?
Semiperipheral development is the idea that that it has mainly been semiperipheral societies that have expanded networks, made larger states, and innovated and implemented new techniques of power and new productive technologies that have transformed the very logic of social change. Semiperipheral societies are those that are out on the edge of the older core polities in an interpolity system – a system of allying and fighting polities. The hypothesis of semiperipheral development asserts that semiperipheral regions in core-periphery hierarchies are fertile sites for innovation and the implementation of new institutions that sometimes allow societies in these regions to be upwardly mobile and/or to transform the scale (and sometimes the qualitative nature) of institutional structures.  This is not simply the notion that core traits diffuse toward the periphery. It is rather the idea that semiperipheral innovation enables upward mobility and occasionally transforms whole systems. Semiperipheral actors have taken different forms in different systems. Semiperipheral marcher chiefdoms and semiperipheral marcher states conquered older core polities to form new larger core-wide polities. Semiperipheral capitalist city-states exploited opportunities to accumulate wealth from trade and the production of commodities. And in the modern world-system it is semiperipheral nation states that have risen to become hegemonic.
The hypothesis of semiperipheral development presumes a cross-cultural conceptualization of core/periphery hierarchies in which more powerful societies importantly interact with less powerful ones. The idea of core/periphery hierarchy was originally developed to describe and account for the stratified relations of power and dependency among societies in the modern world-system. The comparative world-systems approach developed by Chase-Dunn and Hall (1997) distinguishes between core/periphery differentiation, in which there is important interaction among societies that have different degrees of population density, and core/periphery hierarchy in which some societies are dominating and/or exploiting other societies. It is not assumed that all world-systems have core/periphery relations. Rather this is a research question to be determined in each case.
Settlement Systems of Nomads
Big game hunting is not a natural pursuit. But it is fun, dangerous and rewarding as long as there are large edible animals that can be killed and eaten. McNeill and McNeill (2003) describe humans as the “weed species” because our use of symbols and tools has allowed us to specialize in adaptability. We can move into new niches and can adjust to environmental changes more rapidly than any other megafauna (even coyotes!). If there are big edible animals to be hunted, even people who know how to fish and farm will cease these activities until the large and roastable beasts have been depleted (or extinguished) (Kirsch 1984) (see Figure 1). Big game hunters moved rapidly into territories that were rich in large huntible and tasty animals. In two known instances (Australia about 40,000 years ago, and the New World about 12,000 years ago) the arrival of the hunters was followed within two thousand years by the extinction of many species of megafauna. It is hard to believe that these extinctions were completely caused by human hunting, but that was undoubtedly part of the story.
The arrival and spread of “paleoindians” in North America is signaled by a distinctive “Clovis-style” lithic projectile point, a 5-cm. spear point with a fluted face that was used at the end of a long spear to kill large animals such as mastadons and elk. This distinctive projectile point is found all over North America, and it is believed that the paleoindians followed herds in very large and rather regular annual migration circuits. The migrating bands would come together annually in a place with sufficient food stocks to allow for a big gathering, and often adjacent to quarries
Figure 1: Polynesians in New Zealand hunt flightless moa to extinction (Kirch 1984)
where the kinds of stone used to make Clovis points were procured (see Figure 2). The broadly similar nature of the projectile point style indicates a “cultural” similarity that is continental in size (Kowalewski 1996), and this is in contrast to what happened next in the archaeological record. As big game began to be depleted and declined due to climate change, the people turned to the exploitation of smaller species and greater reliance on vegetable gathering and marine resources. Hunting continued, and the atlatl, a wooden spear thrower, was used to throw shorter spears farther. Projectile points became smaller, and distinctive regional styles emerged.
Figure 2: Paleo and archaic migration circuits
Archaeologists contend that this shift toward more diversified foraging corresponded with somewhat spatially smaller and more regular annual migration circuits (Fagan 1991). People began developing regional identities and restricting their migrations to smaller and more densely occupied territories (see Figure 2). Sedentism had not yet emerged, but the transition from larger circuits to smaller circuits and more diversified foraging was already a move in the direction of sedentism. We were already moving down the food chain in order to accommodate a larger population.
The First Villagers
It is commonly believed that all hunter-gatherers were nomadic and that sedentism emerged with planting during the “neolithic revolution.” But this is wrong. Sedentism emerged before the neolithic revolution among diversified foragers, and sedentary foraging societies survived into recent modernity in certain ecologically abundant locations such as California and the Pacific Northwest. Some hunter-gatherers in prime environments figured out how to exploit less vulnerable natural resources such as seeds, tubers, small game, and fish. They were able to live in permanent villages without depleting the environment.
The term “mesolithic” usually refers to hunter-gatherers who live in more or less permanent settlements -- more or less, because many mesolithic diversified foragers lived in a winter village and then moved to other locations during the summer for seasonal hunting or gathering. The transition from nomadism to sedentism was a matter of seasonal camps becoming occupied for longer and longer periods of time, and with some of the population remaining while others went off to other locations during special seasons. The earliest sedentary societies were of diversified foragers in locations in which nature was bountiful enough to allow hunter-gatherers to feed themselves without migrating. These first villagers continued to interact with still-nomadic peoples in both trade and warfare. The most well known of these is the Natufian culture of the Levant, villagers who harvested natural stands of grain around 11,000 years ago.
In many regions the largest villages had only about 250 people. In other regions there were larger villages, and regions with different population densities were often in systemic interaction with each other (Chase-Dunn and Mann 1998). Settlement size hierarchies emerged when a village at a crucial location, often the confluence of two streams, became the home place of important personages and the location of larger ritual spaces such as sweat lodges. Sedentary foragers developed long-distance trading networks, and the shift from nomadism to sedentism can be understood as a transition from a system in which people move to resources to one in which resources are moved to people.
The purely spatial aspects of this transition are also interesting. As we have seen above in the description of the emergence of smaller seasonal migration circuits and regionally differentiated tool styles, nomadic systems went from very large to smaller, and to very small with the emergence of sedentism. But the settlement systems of sedentary peoples began again to get larger, because trade networks emerged to link settlements and peoples that were distant from one another (see Figure 3). These trade networks grew and grew, though they also occasionally shrank, a repeating pattern that Chase-Dunn and Hall (1997) have called “oscillation.” Eventually the systemic interaction networks became global (Earth-wide) in extent, and it is then that we call them globalization. But networks shrank with the coming of sedentism, and then expanded again to become completely global with the arrival of oceanic voyaging.
Figure 3: Spatial networks shrank and then expanded with the emergence of sedentism
Human ecologists and anthropologists often study settlement-subsistence (ecosettlement) systems to understand the connections between human social organization and the environment. Subtle differences in ecosettlement systems can also be useful for understanding the relationships between adjacent groups. In prehistoric Northern California the Wintu and Yana peoples were both sedentary foragers, but there were important differences in their settlement and subsistence patterns. The Wintu lived along large rivers on the Sacramento valley floor and made seasonal treks up into the foothills and mountains (see Figure 4), while the Yana had their villages on smaller waterways in the foothills and made Fall visits to the valley floor and summer visits to the mountains (see Figure 5). The Yana villages were smaller than those of the Wintu. The Yana relied more completely on deer hunting, whereas the Wintu greatly relied on fishing, especially the seasonal harvest of migrating salmon (Chase-Dunn and Mann 1998). Interactions between the Yana and the Wintu were often conflictive, but there is little evidence that the more populous Wintu were exploiting or dominating the Yana. This was a case of core/periphery differentiation, but not core/periphery hierarchy.
Figure 4: Valley-dwelling Wintu settlement and subsistence (Clewett 1984)
Figure 5: Hill-dwelling Yana settlement and subsistence (Clewett 1984)
The spatial aspect of population density is one of the most fundamental variables for understanding the constraints and possibilities of human social organization. The “settlement size distribution” – the relative population sizes of the settlements within a region-- is an important and easily ascertained aspect of all sedentary social systems. And the functional differences among settlements are a basic feature of the division of labor that links households and communities into larger polities and interpolity systems. The emergence of social hierarchies is often related to size hierarchies of settlements. And the building of monumental architecture in large settlements has been closely associated with the emergence of more hierarchical social structures – complex chiefdoms and early states.
The spatial relationships among settlements in a region and there relative sizes can be seen from archaeological evidence, and so this is an empirically useful pattern that allows us to compare preliterate systems with those for which we have documentary evidence. Figure 6 below contains Hans Nissen’s drawings of 1-tiered, 2-tiered, 3-tiered and 4-tiered settlement size hierarchies.
Settlement size distributions are often graphed to show the relative population sizes of the settlements in a region. Figure 7 shows a steep settlement size distribution in which the largest settlement is much larger than the second largest, and a flat distribution in which all the settlements are about the same size. Urban geographers suggest that a spatial size hierarchy is related to the distribution of functions across settlements and transportation costs (Christaller 1966). Goods and services that can easily be distributed across a whole region from a central point will be located in the largest central settlement, whereas products that cannot easily be stored or transported will be produced locally in all the smaller settlements. The “range of goods” creates the space economy. This approach was developed to describe market societies, but it may also be relevant for understanding settlement systems in which exchange is organized as reciprocity, because transportation costs must be taken into account in the effort to be generous.
Urban geographers contend that there is a tendency for settlement size hierarchies to approximate a rank-size or lognormal size distribution. A rank-size distribution exists when the 2nd largest settlement is ½ the size of the largest, the 3rd largest is 1/3 the size of the largest, and etc. A lognormal distribution is similar in shape. It exists when the ranked population sizes of settlements in a region fall on a straight line
Figure 6: Settlement size hierarchies (Nissen 1988:42)
when the population sizes have been transformed to a logarithmic scale. “Urban primacy” is said to exist when the largest city in a region is larger than would be expected based on the rank-size or lognormal distributions. Empirical studies have shown that many city size hierarchies do approximate the rank-size rule, but some are flat (as with a 1-tiered size distribution) and many are primate (e.g. Chase-Dunn 1985b).
The original mesolithic invention of relatively permanent village life was made possible by a diversified foraging strategy that mixed the gathering of vegetable resources, fishing and hunting of small game. This developed in a context in which the villagers continued to cooperate and compete with more nomadic hunter-gatherers. The Natufian culture of the Levant is the earliest known example of mesolithic sedentism based on diversified foraging – this around 9000 BCE (Bar-Yosef and Belfer-Cohen 1991; Moore 1982). Sedentary foragers probably invented fairly closely specified territorial boundaries as
well as a more active intervention in the productive cycles of nature. Sedentism also had a positive effect on population growth. Families living in permanent villages could afford to have more closely spaced children than nomadic peoples could manage (McNeill and McNeill 2003). Both nomadic and sedentary foragers are known to have used fire to increase the growth of food-producing plants and grazing areas attractive to game. This kind of activity has been called “protoagriculture” (Bean and Lawton 1976).
Naturally occurring stands of
Figure 7: Flat and steep settlement size distributions
grain were less productive in the smaller valleys in the hills adjacent to the prime gathering regions of the Natufian peoples. It is plausible that when the nomads in these neighboring regions tried to emulate the sedentary life-style of the mesolithic villagers, they found that these less abundant natural stands were quickly eaten up, and so they experimented with planting the seeds that they had gathered in order to increase the productivity of their lands. The proto-horticulture of the diversified foragers may have morphed into true horticulture in the hands of the adjacent neighbors of the original sedentary foragers (Hayden 1981). The first instance of semiperipheral development may have been the emergence of a new productive technology (planting) in a region adjacent to one in which an earlier new departure had occurred (sedentism).
Figure 8: A 3-tiered settlement size hierarchy
The techniques of gardening spread both west into the valley of the Nile and east toward Mesopotamia. Gardening increased the number of people that could be supported by a given area of land, making greater population density possible. Community sizes grew in rain-watered regions and population growth led to the migration of farmers away from the original heartland of gardening. Horticultural techniques also diffused from group to group and were combined with the domestication of pigs, sheep and goats. Domestication of animals and the use of milk as well as meat eventually made it possible to move a few notches back up the food chain, reversing some of the descent that followed the depletion of big game. Still-nomadic hunter-gatherers traded with the Neolithic towns, and new forms of pastoral nomadism developed based on the herding of domesticated animals.
The simple model here is that technological development (planting) increased population density and this facilitated the emergence of larger settlements and social hierarchies. McNeill and McNeill (2003) note that state formation in East Asia followed the spread of rice cultivation (e.g. from China to Korea to Japan). They point out that a storable and tradable grain is far more conducive to state formation than are crops that are not easily stored (such as yams). But there is evidence from the Chesapeake region of indigenous North America that adoption of planting does not always immediately lead to greater complexity and hierarchy (Chase-Dunn and Hall 1999).
The arrival of maize planting in the Chesapeake region allowed the formerly mesolithic diversified foragers living in rather large villages to redisperse into widely spread farmsteads, and to reduce the intensity of their trading and ritual symbolization of group identity and social hierarchy. So increasing productivity can, under some conditions, lead to deconcentration and less social hierarchy. The ability to produce a surplus does not automatically lead to hierarchy formation. Surplus production must be possible, but hierarchy formation occurs when population pressures lead to conflict. In the case of the Chesapeake, the arrival of maize reduced population pressure and so those hierarchies and larger villages that had already emerged went into decline. It was not until population pressure had returned after a period of population growth that villages and hierarchies grew again. New hierarchies emerge to regulate access to scarce resources and to reduce the intensity of conflict (Chase-Dunn and Hall 1997:Chapter 6).
As villages eventually grew larger, trade networks did as well and craft specialists began producing for export and importing raw materials. Trade networks expanded and thickened, but not permanently. All networks exhibit a pattern of expansion and contraction (oscillation), and these waves are punctuated by occasional upward sweeps that connect much larger regions. Thus the waves of globalization and deglobalization that have been shown to have occurred in the last 150 years (Chase-Dunn, Kawano and Brewer 2000), are only the most recent and largest instances of a much older pattern of network expansion and contraction.
To the Flood Plain
Uruk, built on the floodplain between the Tigris and Euphrates Rivers about 5000 years ago, was the first large settlement that we call a city. Other cities soon emerged on the floodplain and this first system of cities developed in a region that had already seen hierarchical settlement systems of villages based on complex chiefdoms. For seven centuries after the emergence of Uruk, the Mesopotamian world-system was an interactive network of city-states competing with one another for glory and for control of the complicated transportation routes that linked the floodplain with the natural resources of adjacent regions.
According to Nissen (1988:Chapter 3) the first three-tiered settlement system in Southwest Asia emerged on the Susiana Plain (in what is now Iran adjacent to the Mesopotamian flood plain) in the Ubaid period (5500-4000 BCE). This would indicate the presence of complex chiefdoms, and Wright (1986) points to the importance of the existence of complex chiefdoms in a region as the necessary organizational prerequisite for the emergence of pristine states. In other words, first states did not emerge directly from egalitarian societies. Evidence from Uqair, Eridu and Ouelli shows that there were also Ubaid sites on the Lower Mesopotamian flood plain that were as large as the sites on the Susiana Plain at this time. The Early Ubaid phase at Tell Ouelli shows remarkably complex architecture as early as anything on the Susiana Plain. Thus there was an interregional interaction system of chiefdoms based on a mix of rain-watered and small-scale irrigated agriculture.
In the next period (Uruk or Late Chalcolithic from 4000-3100 BCE) the first true city (Uruk) grew up on the floodplain of lower Mesopotamia, and other cities of similar large size soon emerged in adjacent locations. Uruk had a peak population of about 50,000. Surrounding these unprecedentedly large cities were smaller towns and villages that formed the first four-tiered settlement systems (Adams 1981). This was the original birth of “civilization” understood as the combination of irrigated agriculture, writing, cities and states. States also emerged somewhat later in the Uruk period on the Susiana Plain (Wright 1998 and these also developed four-tiered settlement systems (Flannery 1998:17). This was an instance of uneven development -- the transition from an inter-regional interchiefdom system to an inter-city-state system that emerged first in Mesopotamia and then spread to the adjacent Susiana plain.
Both cities and states got larger with the development of social complexity, but they did not grow smoothly. Rather there were cycles of growth and decline and sequences of uneven development in all the regions of the world in which cities and states emerged. It was the invention of new techniques of power and production that ultimately made possible the more complex and hierarchical societies that emerged. The processes of uneven development by which smaller and newer semiperipheral settlements overcame and transformed larger and older ones has been a fundamental aspect of social evolution since the invention of sedentary life. And social evolution is analogous to ecological succession. Higher levels of complexity cannot emerge directly out of low levels. Production of surplus and the formation of chiefdoms must form the organizational soil out our which state formation can grow. But states do not form automatically. They are the products of human innovation in a situation in which they have been made possible by earlier developments, and in which they can solve problems that are posed under current conditions. Thus there is a degree of historical contingency and agency in the process, and this is very evident in the pattern of semiperipheral development, because it is not all semiperipheries that make the leap.
Sedentary societies interacted with still-nomadic societies from the beginning of sedentism, and archaeologists have studied farmer-forager interactions in many contexts. This may have been the original core/periphery division of labor. We have suggested above that it was nomadic neighbors of the sedentary Natufian foragers who may have first developed planting when they sought to emulate the village life of the Natufians. This may have been the earliest instance of semiperipheral development.
As sedentary societies expanded horticulture, they domesticated both plants and animals, especially in ancient Southwest Asia and Egypt. Domesticated wheat and barley hold there grains longer and are easier to harvest than the wild varieties. Foragers had lived with dogs for millennia, but goats, sheep, pigs, cattle, donkeys, horses and cattle were domesticated by either sedentary peoples, or by nomadic peoples who became pastoralists in interaction with sedentary farmers. Nomadism co-evolved with sedentism, a process most famously described for East and Central Asia by Owen Lattimore (1940). And nomadic pastoralists played an important role in the formation of sedentary states and empires because they not only supplied meat and animal products, but they soon underwent political evolution as well. The Central Asian steppe nomad confederacies were able to mobilize large cavalries to attack agrarian empires, and they both pillaged and extracted tribute in a process most clearly described by Thomas Barfield (1989). It was also former nomadic pastoralists who formed semiperipheral states on the edges of old core regions, and who were the protagonists of empire formation when they conquered adjacent core states. Thus did the dynamics of sedentary/nomadic relations play an important role in the evolution of the tributary mode of accumulation.
What is the relationship between the size of settlements and power in intergroup relations? Under what circumstances does a society with greater population density have power over adjacent societies with lower population density, and when might this relationship not hold? Population density is often assumed to be a sensible proxy for relative societal power. Indeed, Chase-Dunn and Hall employ high relative population density as a major indicator of core status within a world-system (Chase-Dunn and Hall 1997). But Chase-Dunn and Hall are careful to distinguish between “core/periphery differentiation” and “core/periphery hierarchy.” Only the latter constitutes actively employed intersocietal domination or exploitation, and Chase-Dunn and Hall warn against inferring power directly from differences in population density.
In many world-systems military superiority is the key dimension of intersocietal relations. Military superiority is generally a function of population density and the proximity of a large and coordinated group of combatants to contested regions. The winner of a confrontation is that group that can bring the larger number of combatants together quickly. This general demographic basis of military power is modified to some extent by military technology, including transportation technologies. Factors such as better weapons, better training in the arts of war, faster horses, better boats, greater solidarity among soldiers and their leaders, as well as advantageous terrain, can alter the simple correlation between population size and power.
Ironically, George Modelski’s (2003) important study of the growth of world cities completely ignores the growth of states and empires, though Modelski is himself an astute scholar of international relations and geopolitical power. Modelski contends that cities are the most important driving force of world system evolution and that we may conveniently ignore states and empires. The relationship between political power and settlements itself evolved over the millennia, so that analysis of the relationship between size and power is necessary in order to understand what happened.
The most important general exception (in comparative evolutionary perspective) to the size/power relationship is the phenomenon of semiperipheral development mentioned above. The pattern of uneven development by which formerly more complex societies lose their place to “less developed” societies takes several forms depending on the institutional terrain on which intersocietal competition is occurring. Less relatively dense semiperipheral marcher chiefdoms conquer older core chiefdoms to create larger chiefly polities (Kirch 1984). Likewise, semiperipheral marcher states, usually recently settled peripheral peoples on the edge of an old region of core states, frequently are the agents of a new core-wide empire based on conquest (Mann 1986; Turchin 2003).
Another exception is the phenomenon of semiperipheral capitalist city-states – states in the interstices between tributary empires that specialized in long-distance trade and commodity production. Though these were rarely the largest cities within the world-systems dominated by tributary empires, they played a transformational role in the expansion of production for exchange and commodification in the ancient and classical systems. And less dense semiperipheral Europe was the locus of a virile form of capitalism that condensed in a region that was home to a large number of unusually proximate semiperipheral capitalist city-states. This development, and the military technology that emerged in the competitive and capitalist European interstate system, made it possible for less dense Europe to erect a global hegemony over the more densely populated older core regions of Afroeurasia (Chase-Dunn and Hall 1997). The more recent hegemonic ascent of formerly semiperipheral national states such as England and the United States are further examples of the phenomenon of semiperipheral development.
The phenomenon of semiperipheral development does not totally undermine the proposition that societal power and demographic size are likely to be correlated. What it implies is that this correlation can be overcome by other factors, and that these processes are not entirely random. Denser core societies are regularly overcome or out-competed by less dense semiperipheral societies, but it does not follow that all semiperipheral or peripheral regions have such an advantage. On the contrary, in most world-systems most low-density societies are subjected to the power of more dense societies. Semiperipheral development is a rather important exception to this general rule.
Why should a city system have a steeper size distribution when there is a greater concentration of power? The simple answer is that large settlements, and especially large cities, require greater concentrations of resources to support their large populations. This is why population size has itself been suggested as an indicator of power (Taagepera, 1978a: 111). But these resources may be obtainable locally and the settlement size hierarchy may simply correspond to the distribution of ecologically determined resources. People cluster near oases in a desert environment. In such a case it is not the political or economic power of the central settlement over surrounding areas that produces a centralized settlement system, but rather the geographical distribution of necessary or desirable resources. In many systems, however, we have reason to believe that relations of power, domination and exploitation do affect the distribution of human populations in space. Many large cities are as large as they are because they are able to draw upon far-flung regions for food and raw materials. If a city is able to use political/military power or economic power to acquire resources from surrounding cities, it will be able to support a larger population than the dominated cities can, and this will produce a hierarchical city size distribution.
Of course the effect can also go the other way. Some cities can dominate others because they have larger populations, as discussed above. Great population size makes possible the assembly of large armies or navies, and this may be an important factor creating or reinforcing steep city size distributions.
The relationship between power and settlement systems is contingent on technology as well as political and economic institutions. Thus the relationship between urban growth and decline sequences and the growth/decline sequences of empires varies across different systems or in the same regional system over time as new institutional developments emerge. We know that the development of new techniques of power, as well the integration of larger and larger regions into systems of interacting production and trade, facilitate the emergence of larger and larger polities as well as larger and larger cities. Thus, there is a secular trend at the global level and within regions between city sizes and polity sizes over the past six millennia.
Studies of the relationship between the rise and fall of empires and the growth/decline phases of the largest cities in the same regions have found differences in the temporal relationship between the growth and decline of largest cities and largest empires. Partial correlations that take out the long-term trend show that the medium-term relationship between city and empire growth is significantly positive in Mesopotamia (2800 BCE-650 BCE), South Asia (1800 BCE-1500 CE) and Europe (430 BCE-1800 CE), but not in Egypt, West Asia, and East Asia (Chase-Dunn, Alvarez and Pasciuti 2005: Table 5.2). In the regions in which there are significant correlations this is sometimes due to the big empires building their own big capital cities, but at other times a big city appears in the region that is outside of the largest empire. This suggests that regions go through general phases of expansion and contraction in which both cities and empires grow and then decline, and this supposition is confirmed by the finding in all regions of high partial correlations between the growth/ decline phases of largest and second largest cities (Chase-Dunn, Alvarez and Pasciuti 2005: Table 5.3), and rather surprisingly, a similar set of significant positive partial correlations in all five regions studied between the growth/decline phases of largest and second largest empires (Chase-Dunn, Alvarez and Pasciuti 2005: Table 5.4). This latter is surprising because territorial growth is a zero sum game among adjacent empires, and yet the medium-term temporal correlations are positive, indicating that empires get larger and smaller together within regions. This is strong evidence that regions experience cycles of growth and decline that affect both cities and states.
Synchronous East/West Growth-Decline Phases
Earlier studies have used data on both city sizes and the territorial sizes of empires to examine the hypothesis that regions distant from one another experienced synchronous cycles of growth and decline (e.g. Chase-Dunn and Willard 1993; Chase-Dunn, Manning and Hall 2000; Chase-Dunn and Manning 2002). Frederick Teggart’s (1939) path-breaking world historical study of temporal correlations between events on the edges of the Roman and Han Empires argued the thesis that incursions by Central Asian steppe nomads were the key to East/West synchrony. An early study of city-size distributions in Afroeurasia (Chase-Dunn and Willard 1993; see also Chase-Dunn and Hall 1997: 222-223) found an apparent synchrony between changes in city size distributions and the growth of largest cities in East Asia and West Asia-Mediterranean over a period of 2000 years, from 500 BCE to 1500 CE. That led to and examination of data on the territorial sizes of empires for similar East/West synchrony, which was found (Chase-Dunn, Manning and Hall 1999). The empire size data also allow the examination rise and fall sequences of large empires in South Asia, but these are not synchronous with the growth/decline phases of empires in East Asia or West Asia (Chase-Dunn, Manning and Hall 1999). Chase-Dunn and Manning (2002) have re-examined the city size data using constant regions rather than political-military networks to see if the East/West synchronous city growth hypothesis holds when the units that are compared are somewhat different. Their results confirm the existence of East/West city growth/decline synchrony. From 500 BCE until 1500 CE, when the largest city in East Asia was growing, the largest city in the West Asia/Mediterranean region was also growing, and this also holds for empires (see Figure 9).
Figure 9: Sizes of Largest cities in East Asia and West Asia/Mediterranean
Comparable other instances of distant systems that came into weak contact with one another can be found. Within the Old World, the Mesopotamian and Egyptian core regions were interacting with one another by means of prestige goods exchange from about 3000 BCE until their political-military networks (state systems) merged in 1500 BCE. Chase-Dunn, Pasciuti, Alvarez and Hall (forthcoming) have already examined this case for synchrony and have not found it, though the data on Bronze Age city and empire sizes are very crude with regard to temporality and accuracy. It is also possible to study the temporality of rise and fall and oscillations among distant regions in the New World (e.g. Peregrine 2005).
The East/West growth/decline synchrony seems to be rather robust, though better estimates and finer temporal resolution of empire and city sizes might challenge it. Interregional synchrony can be caused when two cyclical processes get simultaneously reset, either by the same cause or by different causes. This could be a one-shot occurrence. Or a process that is similarly cyclical can cause synchrony. Candidates for the East/West synchrony are: climate change, epidemic diseases, trade interruptions, or attacks by Central Asia steppe nomads. Sorting this out will require data on these for the relevant regions over the relevant time period. At present we have located time series data on climate change in China, and it does not seem to be at all related to the East Asian rise and fall of empires. If this is true, then logically climate change can be ruled out as a cause of interregional empire synchrony.
Cities and Social Evolution
George Modelski’s World Cities, -3000 to 2000 examines human social evolution over the past 5000 years by focusing on the growth of world’s largest cities and also presents to results of a huge empirical effort to expand our knowledge of the population sizes of the largest settlements since the Bronze Age. The growth of cities is a useful indicator of world system evolution because the ability of a society to produce and maintain a large settlement is a major accomplishment. We can trace the emergence of social complexity by knowing where the largest human settlements are at any point in time. Beginning with Uruk, Modelski traces the emergence and spread of large cities from Mesopotamia and Egypt to East Asia, South Asia, Europe and the Americas.
Regarding the city population data, Modelski has extended and improved the work of that most eminent coder of city sizes, Tertius Chandler (1987). For students of urban and world history this work is of immeasurable value. Modelski has labored hard to produce the best published comprehensive compilation of estimates of city population sizes now available. His careful improvement upon earlier efforts to estimate the population sizes of ancient cities is a huge step forward. He uses estimates of the built-up area of a city and a population density factor (Modelski 2003:11 and Note 5 on p. 17) to estimate the population sizes. He adds considerable depth, especially to the coverage of the Bronze Age.
In the “ancient era” (-3000 to –1000) Modelski defines world cities as those that reach a population size of 10,000 or more. In the following “classical era” (-1000 to 1000) cities must be at least 100,000 in population size to count as world cities. And in the modern era (since 1000) the cut-off point is one million. Modelski observes a phenomenon, also noticed by Roland Fletcher (1995), that a few cities are the first to reach a whole new scale, and then a size ceiling is encountered during which cities in other regions catch up to the new scale. The current maximum seems to be around twenty millions and the phenomenon of catching up is now occurring. Some of the world’s largest cities are now in developing countries such as Mexico, Brazil, India and China.
Modelski’s study of the phases of urbanism is convincing regarding the contention that urbanization has been neither random nor linear. Instead it has followed a recurring pattern of rapid growth followed by slow growth or decline. A phase of fast growth concentrated in one or a few regions is followed by slower growth and the diffusion of large cities to other areas. Rapid and concentrated growth was followed by leveling off and dispersal due to “countervailing forces.” These countervailing forces emerged from what Modelski terms the “Center-Hinterland” divide of a regional world system. The first growth phase emerged in a center that eventually encountered limits to growth from resource exhaustion, environmental stress and “failures of knowledge.” The leveling process occurred as these limits were reached, weakening the old center. Incursions from the hinterland increased, taking advantage of the center’s weakness. This allowed the semi-hinterland, a region adjacent to the old center with smaller cities, to catch up to the urban scale of the old center.
Modelski also compares his phases of urban growth with existing estimates of overall population size and growth. He finds that the overall population growth phases correspond in time with the urban expansions of the three eras. This study leads to what Modelski calls a “manifest case of evolution.” The three phases of urbanization correspond to periods of world system evolution: cultural, social and political. The ancient cultural phase saw the creation of a learning structure based on cities, writing and calendars, resulting in a platform for sustained and intensified human interaction on a large scale. The classical social phase brought about a more extensive, inclusive and integrated system. Expanding during Karl Jasper’s “ Axial Age,” the cities of the classical period can be grouped according to the world religions that dominated social structures during that era. The modern political phase poses choices regarding an evolutionarily stable structure of world organization. Modelski predicts that the future fourth phase will be an economic one that will see a “stabilization and consolidation of the economic and material basis” of world society.
Figure 10: Sumerian Ur
From the point of view the structure of population density both ancient and most modern industrial cities conform to the same concentric volcano model. A central non-residential district (business or monumental or both) is surrounded by concentric rings of decreasing density, with low-density suburbs as the outer ring. This is the basic structure of nearly all cities from the beginning in Mesopotamia 5000 years ago, to most cities in the world today that were built before the advent of the automobile (see Figure 11).
Figure 11: The volcano model of urban population density
Figure 12: Low density postmodern city structure (Dear 2001).
There were earlier low-density cities, but they were rare. Angkor Wat, the gigantic capital of the Khmer state in Cambodia, was a city of farmlets with a large monumental center. Each residence had a tract of farmland for a yard, with canals linking a huge area. There were no high-density residential quarters. But this was an unusual exception to the volcano model. In the contemporary world older volcano cities are being surrounded and linked together by post-modern suburbs, so-called “edge cities” (Garreau 1991).
Figure 13: Suburban sprawl at Levittown
The problem of sustainable urbanization is crucial for the human encounter with the consequences of our ballooning environmental footprint. Over half of the human population of the Earth now lives in very large cities, and these have spread rapidly over the land as population densities within cities have decreased and cities have spread into huge city-regions. The system of world cities has been flattening as megacities in the non-core countries have caught up in terms of overall population size with the global cities of the core.
Changes in the global city size distribution, especially its flattening as megacities have emerged in the non-core, has important implications for theories of urban growth, globalization and the future of global inequalities. This section considers the conceptualization of world cities and city-regions and the idea of a global system of cities. I shall consider the global city-size distribution and the implications of its flattening for the question of the limits of settlement size and the problems of how to spatially bound cities and city-regions. And I further discuss the emergence of low density and multicentric cities.
The role of city systems in the reproduction and
transformation of human social institutions has been altered by the emergence
and predominance of capitalist accumulation. Whereas most of the important
cities of agrarian tributary states were centers of control and coordination
for the extraction of labor and resources from vast empires by means of
institutionalized coercion, the most important cities in the modern world have
increasingly supplemented the coordination of force with the manipulations of
money and the production of commodities. 
The long rise of capitalism was promoted by semiperipheral capitalist city-states, usually maritime coordinators of trade protected by naval power. The Italian city-states of Venice and Genoa are perhaps the most famous of these, but the Phoenician city-states of the Mediterranean exploited a similar interstitial niche within a larger system dominated by tributary empires. The niche pioneered by capitalist city-states expanded and became more predominant in the guise of core capitalist nation-states in a series of transformations from Venice and Genoa to the Dutch Republic (led by Amsterdam) and eventually the Pax Britannica coordinated by the great world city of the nineteenth century, London (Chase-Dunn and Willard 1994). Thus did capitalism move from the semiperiphery to the core, constituting a world-system in which the logic of profit making had become more important than the logic of tribute and taxation. In 1900 CE London was still the largest city, but New York was coming up fast (see Figure 14).
Figure 14: The world city size distribution in 1900 CE
Within London the political and financial functions were spatially separated: empire in Westminster and money in the City. In the twentieth century hegemony of the United States these global functions became located in separate cities (Washington, DC and New York).
Thus the role of cities in world-systems changed greatly as capitalism became the predominant mode of accumulation over the last 500 years. In earlier world-systems the biggest cities were empire-cities based on the ability of states to extract resources using institutionalized coercion (armies, bureaucracies, etc.) Capitalist cities existed, but they were in the semiperipheral spaces between the large tributary empires. With the rise of Europe we have capitalist cities becoming the most important cities in the whole world-system. This is especially obvious with the rise of Amsterdam, London and New York – the world cities of the capitalist era.
Nevertheless, the relationship between power and size continued to operate (until recently) in the modern system. Figure 15 displays changes in the city size distribution of the largest cities in the European-centered world-system since 800 CE (Chase-Dunn 1975). The city size distribution of interstate systems is almost always flatter that the size distributions of settlements within a single polity, because the multicentric political structure of interstate systems affects the size distribution of settlements. Figure 15 uses the “Standardize Primacy Index,” a measure of deviation from the lognormal rule (Walters 1975). As can be seen, the Europe-centered city system is never steeper than the lognormal distribution. And it is occasionally much flatter. The periods of flatness mainly correspond with times of political decentralization in which there was an absence of a hegemonic core power (Chase-Dunn and Willard 1994).
One possible explanation for the recent descent into flatness of the world city size distribution is the declining hegemony of the United States. But there are also other possibilities, such as the 20 million-size ceiling posited by Fletcher discussed below.
Figure 15: The city-size distribution of the Europe-centered system, 800 to 1975 CE
The great wave of globalization in the second half of the twentieth century has been heralded (and protested) by the public as well as by social scientists as a new stage of global capitalism with allegedly unique qualities based on new technologies of communication and information processing. Some students of globalization claim that they do not need to know anything about what happened before 1960 because so much has changed that the past is entirely non-comparable with the present. Most of the burgeoning literature on global cities and the world city system shares this breathless presentism. All social systems have exhibited waves of spatial expansion and intensification of large interaction networks followed by contractions. The real question is which aspects of the most current wave are unique and which are functional repetitions of earlier pulsations. The only way to sort this out is to compare the present with the past.
According to the theorists of global capitalism it was during the 1960’s that the organization of economic activity entered a new period expressed by the altered structure of the world economy: the dismantling of industrial centers in the United States, Europe and Japan; accelerated industrialization of several Third World nations; and increased internationalization of the financial industry into a global network of transactions (Sassen 1991). With the emerging spatial organization of the new international division of labor, John Friedmann identified a set of theses known as the “world city hypotheses” concerning the contradictory relations between production in the era of global management and political determination of territorial interests (Friedmann 1986).
Saskia Sassen and others have further elaborated the “global city hypotheses.” Global cities have acquired new functions beyond acting as centers of international trade and banking. They have become: (1) concentrated control locations in the world-economy that use advanced telecommunication facilities, (2) important centers for finance and specialized producer service firms, (3) coordinators of state power, (4) sites of innovative post-Fordist forms of industrialization and production, and (5) markets for the products and innovations produced (Sassen 2001a, 2000, 1991; Brenner 1998; Yeoh 1999; Hall 1996; Friedmann 1995). These structural shifts in the functioning of cities have “impacted both the international economic activity and urban form where major cities concentrate control over vast resources, while financial and specialized service industries have restructured the urban social and economic order” (Sassen 1991: 4). During the 1990’s New York became specialized in equity trading, London in currency trading, and Tokyo in size of bank deposits (Slater 2004).
Beaverstock, Smith and Taylor (1999) use Sassen’s focus on producer services to classify 55 cities as alpha, beta and/or gamma world cities based on the presence of accountancy, advertising, banking/finance and law firms. 
Figure 14: Alpha, beta and gamma world cities according (Beaverstock, Smith and Taylor 1999)
The most important assertion in the global cities literature is the idea that the global cities are cooperating with each other more than the world cities did in earlier periods. The most relevant earlier period is the Pax Britannica, especially the last decades of the nineteenth century. If this hypothesis is correct the division of labor and institutionalized cooperative linkages between contemporary New York, London and Tokyo should be greater than were similar linkages between London, Paris, Berlin and New York in the nineteenth century.
Another important hypothesis of the global cities literature is based on Saskia Sassen’s (1991) observations about class polarization and the casualization of work within globalizing cities. The research of Gareth Stedman Jones on Irish immigration into London’s East End in the mid-nineteenth century (Jones 1971) shows that a somewhat similar process of “peripheralization of the core” was occurring during the Pax Britannica.
Much of the research on the global city system has been based on case studies of particular cities that seek to identify the processes leading to their emergence and positioning within the larger system (Baum 1997; Grosfoguel 1995; Todd 1995; Machimura 1992; Kowarick and de Mello 1986). Janet Abu-Lughod (1999) traces the developmental histories of New York City, Chicago, and Los Angeles through their upward mobility in the world city system. While these U.S. metropoles share similar characteristics with other world cities, they have substantial differences in geography, original economic functions, transportation, and political history to serve as fascinating cases for comparative analyses of globalization.
Types of Suburbanization
From the ancient world until the industrial age most cities had a monumental non-residential center surrounded by high-density residential districts, the “volcano model” described above. Walled cities enclosed these high-density residences, but when the cities grew, suburban districts of rather lower densities formed outside of the old wall. This concentric circle pattern continued to characterize cities in the industrial age despite the geometric decline of transportation costs produced by the steam-powered railways. It was only when new cities were built during the automobile age that multicentric and low-density cities such as Los Angeles emerged (Dear 2000; 2002).  The low-density and multicentric pattern is added to old concentric-style cities when they experience further growth during the automobile age – so-called edge cities.
Thus it is important to distinguish three main types of modern urban macrostructure:
v Type A: concentric-radial cities organized around a central business district with transportation corridors radiating out from it;
v Type B: multicentric low density cities that are mainly “suburban” with relatively small non-residential centers dispersed across the built-up landscape (e.g. L.A.); and
v Type C: a mixture of these two where the older concentric structure has become edged by a newer multicentric and low-density region (so-called edge cities).
Another phenomenon of recent urbanization is the emergence of city-regions, large areas in which big cities are located rather closely to one-another and intervening areas are mainly suburbanized. Urban geographers have noted that populations in the rural areas and small towns of core countries are thinning and people are concentrating in these city regions (Scott 2001; Simmonds and Hack 2000). The city region phenomenon is made plain by examining Figure 17, a global map of city lights at night produced from satellite images (see also Figure 18).
Figure 15: World City Lights Show Urban Regions
Figure 16: City Lights in Europe, North Africa and West Asia
All the continents have city regions, but the largest are the eastern half of the United States and the western portion of Europe, with several other regions also displaying this phenomenon. It is important to develop a method of for spatially bounding multicentric city-regions that will enable us to quantitatively compare these with one another in terms of spatial and demographic sizes, population density, and settlement size distributions and to study differences in their macrourban structures.
The Global City System
It is important to study changes in the global city-size distribution because we are interested in the relationship between cities and power, and because the apparent flattening of the global city-size distribution discovered in the 1980s raises interesting questions about the upper limits of the sizes of megacities. Why did the global city-size distribution flatten out after 1950, modifying a pattern that had existed throughout the British and U.S. hegemonies in which the most powerful country had the largest city and there was a hierarchy of city population sizes revealed by the world’s largest cities (Chase-Dunn 1985)? Roland Fletcher (personal communication) contends that contemporary institutional and infrastructural inventions only allow for megacities to function at maximum populations of around twenty millions and this serves as a kind of ceiling effect which has allowed cities in the non-core to catch up in terms of population size with the largest cities in the most powerful states. This may be what has produced the flat global city-size distribution that emerged after 1950. Another possibility that could account for cities in the semiperiphery catching up with core cities is differences in the demographic transition. Most core countries have achieved a replacement fertility rate, but semiperipheral regions still have a higher fertility rate and faster population growth. This could be a factor is allowing semiperipheral cities to catch up to core cities as regards to population size.
Fletcher’s notion of an upper limit on the sizes of large contiguous cities might also be part of the explanation for the emergence of city-regions rather than gigacities (the logical phase beyond megacities). Another factor that could be at work in producing the size ceiling effect is the emergence of a fairly strong environmental movement within the core. Figure 17 shows Abel Wolman’s plan for delivering water from the Columbia River to Southern California. This
Figure 17: Abel Wolman's (1965) proposal for a canal from the Columbia River to Southern California
scheme was plausible from an engineering standpoint, but is arguably now impossible for political reasons. Lack of cheap water will eventually become a limiting factor on urban growth in Southern California if other factors do not stop it first.
Research on the contemporary global city-size distribution and the phenomenon of city-regions needs to develop methods for spatially bounding cities and city-regions that make use of satellite imagery. Spatially bounding cities using census data has long been problematic because information is often organized in terms of juridical boundaries that do not conform to the real boundaries of cities as built-up areas.
Measurement of the population sizes of cities must address the issue of spatial boundaries. How can we know the number of people who reside in Los Angeles today? We use the most recent census, a survey of “residents” conducted by the U.S. federal government. What are the spatial boundaries of “Los Angeles”? Do we mean the city of Los Angeles, Los Angeles County, the contiguous built-up area that constitutes “greater Los Angeles,” or a definition based on the proportion of the local population that is employed in “Los Angeles”? Does “Los Angeles” include San Diego? Nighttime satellite photos of city lights imply a single unbroken megalopolis from Santa Barbara to Tijuana (see Figure 18). So where is Los Angeles? We use the contiguous built-up area as our main way of spatially defining cities. Urban geographers have made considerable progress on the task of using satellite data to spatially bound cities.
Figure 17: Southern California/Northwestern Mexico conurbation (city lights)
The size and density of city-regions are related to global differences in the level of development, and once these features of city regions are taken into account it may turn out that the global city-region-size hierarchy is related to economic and political/military power as it has been in the past. Developing countries have succeeded in building very large megacities, but their city-regions are not as large and dense as those in the core. Thus once we get the unit of analysis right, city-regions rather than single urban agglomerations, the older association between power and settlement size that characterized the world city system for centuries may turn out to have survived into the current era.
Figure 19 illustrates some of the problems just discussed. It shows the population sizes of the world’s 29 largest cities in 2000 bounded by municipalities rather than urban agglomerations or city regions. Because municipal boundaries vary greatly across cases these numbers are greatly affected by these differences. The apparent difference between Tokyo and New York is a result of not including New Jersey and Long Island as part of greater New York. Nevertheless, the flatness discussed above is apparent in the distribution of sizes from New York on down the list.
Figure 189: World largest cities in 2000 CE (municipal boundaries)
Cities and the Future
of the over six billion people on Earth now live in very large cities. Of
course, large cities are not all the same. Many of the large cities of the
non-core have huge slums where life is tenuous. Inequalities within and between
countries have increased during the most recent wave of globalization, just as
they did in the 19th century wave (O’Rourke and Williamson 2000).
The low-density suburban sprawl that has taken over the process of urban growth
in the core is immensely expensive in terms of resource use. And urbanization
has a huge direct effect on the environment, as cities absorb heat from the sun
and then release it, and humans use energy in cities, which contributes to
global warming. The
”urban heat island” is an important phenomenon that is contributing to global environmental degradation (see Figure 20)
Figure 19: Increasing temperatures in Tokyo, New York, Paris and the world
While core cities have deindustrialized, large cities in the semiperiphery have industrialized and are now the new sites of intense labor struggles (Silver 2003). The global “reserve army of labor” (rural people still not employed in the formal economy) is still large, but continued economic expansion and globalization will eventually incorporate everyone, and the long-run tendency for wages to rise will continue, eventually causing a crisis for capitalism (Wallerstein 2004).
Peter J. Taylor (2003) contends that globalization has decreased the importance of nation-states and increased the importance of cities, and that this may be a good thing because cities are more easily governable by communities of citizens. Human settlement systems have been strongly involved in the processes of social evolution for thousands of years as both cybernetic nodes of innovation, and in the process of semiperipheral development. Regarding the latter, we can expect that new forms of governance relevant to solutions of the emergent problems of the twenty-first century will likely be invented and implemented in the cities of some of the semiperipheral countries, especially Brazil, India, Mexico and China. Curitiba, Brazil has already demonstrated a new form of sustainable urbanism that will become increasingly relevant as the natural resources that have been the basis of sprawl become depleted (Rabinowitz and Leitman 1996)). Democratic socialist regimes that come out of the new labor movements of the semiperiphery are likely to be important supporters of transnational social movements that will contest neoliberal (and neoconservative) global governance and push toward a new kind of globalization from below. The cities of the semiperiphery are fertile spaces for finding solutions for our increasingly urbanized planet.
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 “Polity” is a general term that means any organization with a single authority that exercises sovereignty over territory or a group of people. Polities include bands, tribes and chiefdoms, states and empires. All world-systems are composed of multiple interacting polities. Thus we can fruitfully compare the modern interstate system with earlier systems in which there were tribes or chiefdoms, but no states.
 This notion is further explicated in Chase-Dunn and Hall (1997: Chapter 5).
 As suggested by McNeill and McNeill (2003) climate change may have also played a role in the emergence of gardening. Natural stands of grain depend on rainfall, so a drought would encourage movement to wetter areas and intervention in the natural process of plant growth by sowing.
 Regional and continental differences in “zoological wealth” – the availability of large domesticable animals – had large long-term effects on the speed of the emergence of social complexity (Diamond 1997).
 Pristine or primary state formation is when states first emerge in a region that has no earlier states. Secondary state formation occurs in interaction with existing states. Pristine state formation, like planting, emerged independently in a least five separate regions, demonstrating the existence of a developmental logic thay led to parallel evolution.
 These data are presented in the book and early versions of the data from the ancient period and from East Asia are available from Modelski’s “Evolutionary World Politics” web site at http://faculty.washington.edu/modelski/worldcities.html A somewhat different effort to improve upon Chandler’s compendium is described in Pasciuti and Chase-Dunn (2002) and Pasciuti (2002).
 These cut-off points are used by Modelski to determine the list of world cities during each era, rather than the more conventional approach of studying the largest ten or twenty cities on Earth. The only problem with Modelski’s approach is that, at the beginning of each of his eras the number of cities above the threshold are few, and so information is missing from his dataset on large cities that may be just under the threshold but are still among the largest cities on Earth in that era.
 Obviously military force is still an important element of power in the modern world-system. But the uses of military power have been fundamentally altered by the predominance of capitalist accumulation.
 Peter Taylor and Jon Beaverstock are co-directing the Globalization and World Cities Study Group and Network at Loughborough University. Their website is a valuable resource for the study of systems of world cities (http://www.lboro.ac.uk/gawc/).
 Obviously communications technologies were not as developed in the nineteenth century, though intercontinental telegraph cables had already been laid, and Japan was not yet a core power in the world-system. But the nature and strength of coordination and cooperation among the world cities of the nineteenth century needs to be examined in order to support the hypothesis of greater contemporary integration that the global cities literature assumes.
 Low-density cities also existed in the ancient world. Fletcher (1995) mentions Angkor Wat, Tikal, Great Zimbabwe, Cahokia and Chaco Canyon as examples.
 I suggested something similar in an earlier version of this essay (Chase-Dunn 1992).