Systems of cities are human interaction networks and their connections with the built and natural environments. Logically, the study of city systems is a subcategory of the more general topic of settlement systems. Once humans began living in fairly permanent hamlets and villages it became possible to study the interactions of these settlements with one another. 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. 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 fundamental aspect 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 monumental architecture of large settlements is related to the emergence of more hierarchical social structures - complex chiefdoms and early states.
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 emerged in a region that had already developed hierarchical settlement systems 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. The relationship between cities and states is a fundamental aspect of all complex social systems. The political 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.
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.
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 the most important cities of agrarian tributary states were primarily 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.
A research project at the Institute for Research on World-Systems (University of California, Riverside) is studying the relationships between the growth/decline phases of large cities and the rise and fall of empires over the past 3000 years. The project is also examining the causes of an apparent synchronicity of both city and empire growth/decline phases in East Asian and West Asian/Mediterranean regions from about 650BCE to about 1500 CE (Chase-Dunn, Manning and Hall 2000). More information about this project is available at http://irows.ucr.edu/research/citemp/citemp.html
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. Within London the functions mentioned above 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).
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 joins this breathless presentism. But claims about the uniqueness of contemporary globalization can only be empirically evaluated by studying change over time and by comparing the post-World War II wave of globalization with the great wave of international trade and investment that occurred in the last decades of the nineteenth century. 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. Historical comparison is essential for understanding the most recent incarnation of the system of world cities.
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, it is argued, have acquired new functions beyond acting as centers of international trade and banking. They have become: (1) concentrated command points in the organization of 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 are argued to 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, pg 4). During the 1990's New York has specialized in equity trading, London in currency trading, and Tokyo in size of bank deposits(Slater 2000). 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. 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/)
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.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 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.
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 nineteenth century (Jones n.d.) shows that a somewhat similar process of peripheralization of the core was occurring in the Pax Britannica.
Much of the research on the global city system is 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.
With appropriate data, social network analysis can be a valuable tool for studying the webs of flows and connections among cities, including flows of capital, commodities, information, and people (Smith 2000; Smith and Timberlake 1995). Network analysis produces quantitative indicators of structural characteristics of networks and of nodes (cities) within networks. For example, measures of network centrality are useful for examining the hierarchical aspects of the world city system.Quantitative measurement of the structures of connections and dominance relations among cities-whether these be based on links to global commodity chains, international business, financial and monetary transactions, or critical flows of information, can provide an important window on change over time in the global urban hierarchy (Smith 2000:157). The data necessary for analyzing the structure of the world city system are difficult to obtain because most statistical information is aggregated at the national level rather than at the city level. But researchers are making heroic efforts to locate data on characteristics of and interactions among cities.
Using airline passenger flows between the world's leading cities for 1977-1997 Smith and Timberlake (1998, 2001) offer evidence of change in the structure of the world city system. These data estimate the frequency of face-to-face contacts among corporate executives, government officials, international financiers, and entrepreneurs that grease the wheels of global production, finance, and commerce (Smith 2000).Among other findings, their results place London, New York City, and Tokyo near the top and center of the global city hierarchy, supporting Sassen's views (Smith and Timberlake 1998).Further, while many core cities continue to occupy central positions in the global hierarchy, network roles of other cities have shifted during this time. Latin American world cities have declined in their central positioning and strength in network linkages, while Asian cities and secondary cities on the west coast of the United States (Pacific Rim) have moved into more central positions within the world city system (Smith and Timberlake 2001).
Settlement systems continue to be a fundamental framework for the analysis of social change. The gigacities in both core and semiperipheral countries, and the amazing density of cities on most continents that is revealed by satellite photos of city lights at night would seem to portend Isaac Asimov's Trantor, a planet entirely encased by a single steel-covered city. But the Earthly settlement system may be soon facing sticky wickets that even Asimov did not envision. If the reaction against twentieth century globalization is anywhere near as tumultuous as was the reaction against nineteenth century globalization we are in for a rough ride in the next decades. Whether or not the global cities can keep solidarity among themselves is crucial to all of us, because no one wants new World Wars under contemporary technological conditions. The global village needs to invent mechanisms of integration that can transcend the centrifugal forces that have revisited the modern system of cities frequently in recent centuries.
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*A shorter version of this article will appear in the Encyclopedia of Population, Geoffrey McNicoll and Paul Demeny (eds.) Macmillan, Forthcoming. This is available at http://irows.ucr.edu/research/citemp/setsys/setsys.htm
Figure 1:City lights from satellite photographs
From Hans J. Nissen, The Early History of the Ancient Near East (University of Chicago Press), 1988, p. 41.
Edited and posted on the web on 6th February 2002