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In the 1980s and 1990s, a series of publications, including Saskia Sassen's landmark book The Global City, triggered a new current of research aiming to link a cycle of globalized financial and tech capitalism to a new type of city, analogous to what the industrial city had been in the past. This article first reviews this literature in relation to the history and sociology of the world city. It then reviews criticism and sociological questions advanced by the global city literature and, in particular, research by Saskia Sassen and Manuel Castells. It argues that claims about the uniqueness of the global city were not validated empirically. Nonetheless, the issues this literature raised became central to research on globalizing cities, in particular in relation to the role of finance and financial capitals. Finally, this article argues that different forms of globalization give rise to different types of globalizing cities. A new cycle of research is now underway in relation to the climate crisis and pandemics, as the climate crisis becomes the most important global phenomenon.

LITERATURE CITED

INTRODUCTION

Once upon a time, in the 1970s, sociologists and urban scholars wrote endlessly about the end of cities. New York was bankrupt, many other large Western metropolises were either losing inhabitants or just staying afloat, and metropolises in what was then called the third world were characterized by planners as ungovernable. Polluted fogs were threatening Los Angeles, Mexico City, and London. The industrial crisis provoked massive urban unrest in the northeastern United States (Beauregard 2013) and in European industrial urban regions alike. Processes of deindustrialization revived the dark side of cities: Race riots, urban poverty, empty industrial spaces, crime, and deprivation were on the rise in the inner city or in outer cities. London's punks captured the mood with their "no future" mantra.

The "no future" prophets of cities proved wrong. All around Asia, Latin America, and then Africa, the massive movement toward urbanization transformed the world's urban map, and nonindustrial European and American cities experienced dynamic growth. The majority of the world (close to 60%) is now urbanized, and 800 million people are expected to join cities in the next decade. Megacities like Lagos, Dar es Salaam, Beijing, Tokyo, Shanghai, and Delhi are likely to reach 50 million inhabitants or more before the end of the century, in parallel to the multiplication of small-and medium-sized cities. In 1981, after decades of regular growth interrupted by the crisis of the 1970s, trade figures significantly increased, inaugurating a new cycle of capitalist globalization.

Analyses of cities in relation to globalization processes, in particular labor, trade, and capital, are not new. We have learned from urban historians such as F. Braudel, W. Blockmans, H. Pirenne, and S. Subramanyam that an increase in transnational trade requires hubs and is likely to benefit cities. Sociologists like Karl Marx, Max Weber, and Georg Simmel have produced substantial bodies of research along these lines. The idea of the power and economic influence of some cities is encapsulated in the concept of the world city. The wave of urbanization and the newfound prosperity (together with inequalities) of some major cities in the 1980s revived this concept. Economic models demonstrate this link by showing that agglomeration forces that come from serving global markets in the context of lower trade costs outweigh the peeling away of certain other functions from cities, through comparative advantage forces and global supply chains. The net effect of this push and pull is that some kinds of cities grow-notably large ones that concentrate highly skilled activities with strong agglomeration economies. Despite the pessimism of urban planners and social scientists, many cities have therefore enjoyed considerable economic and demographic growth, leading to what scholars saw as the resurgence of cities (Storper 2013) .

Beginning in the late nineteenth century, the founders of sociology were faced with similar epochal changes. They developed concepts related to the city to make sense of economic, social, cultural, and territorial transformations, concepts that more or less directly addressed the urban question. Examples are Sombart's (1916) typology of cities based on economic activities, Weber's [1978 Weber's [ (1921)) ] conception of the occidental city, Simmel's (1903) analysis of the metropolis, and Park & Burgess's (1925) or Wirth's (1938) conception of the city. From the 1980s onward, planners, economic geographers, sociologists, and economists similarly suggested more or less conceptualized notions: world cities, global cities (a term coined in Sassen-Koob 1984) , megacities, global city regions, megaregions, informational cities, alpha cities, or superstar cities. Scholars such as John Friedmann, Manuel Castells, Saskia Sassen, Allen Scott, Michael Storper, and Peter Taylor conceptualized models of cities, or urban regions, that emerged in relation to globalization processes. Among them, Sassen's (1991) landmark book, The Global City: New York, London, Tokyo, proved the most influential sociological attempt to characterize the changing urban worlds, paving the way for new research all over the world.

The above research on global cities includes many key questions for sociologists (Cohen & Kennedy 2017) . It brings to the fore questions about the denationalization of society, the making of urban societies, the rise of various networks, and the making of transnational social classes and forms of mobility that question the classic national model of society (Urry 2000 , Sheller 2011) . It also raises questions about inequalities, social hierarchies, and migration, which are discussed in Section 4.

This article critically examines the concept of the global city by first revisiting the world city literature and the legacy of world system theory in order to assess the originality of the global city conceptualization (Brenner & Keil 2006) . It then reflects on the major contributions of the debate on the global city from Sassen and Castells. As with Weber's analysis of medieval European cities as complex social formations that became the crucible for the emergence of Western European societies, Sassen (1991) and Castells (1989) saw the global city and the informational city as the centers of globalized capitalism organized by networks, particularly financial networks. Sassen presents global cities as "strategic sites" of the globalized world, allowing broader lessons about social theory to be drawn. However, empirical research triggered by Sassen's ambitious project undermined the global city thesis, suggesting that the processes she identified were common to many globalizing cities. This article argues that the role of finance has been identified by sociologists as the most important factor explaining the peculiarity of global cities in terms of inequality and urban form. Finally, this review argues that globalizing cities are constituted by representations, rankings, and imagination on the one hand and concentrations of migrants and the superrich on the other.

THE GLOBAL CITY: BUILDING ON THE LEGACY OF THE WORLD CITY

One might argue that there is nothing fundamentally new in seeing a relationship between the "global" and the city. This section reviews the classic literature on world cities, mostly from historians and planners, in order to identify the distinct elements of the global city literature. The conceptualization of the global city aims to articulate, not always convincingly, the resurgence of cities within globalization networks and transformations of capitalism. 1 In both conceptualizations, of the world city and of the global city, scholars included the word "city" at a time when neo-Marxist geographers and social theorists inspired by French philosopher/sociologist Henri Lefebvre were abandoning the question of urban society, collective action, labor market, or governance to focus on modes of urbanization or planetary urbanization (Brenner 2013) .

World cities were classically part of nation-states or empires, centers of trade and political capital. The most important ones were also command centers, in that they contained the financial apparatus allowing use of the massive profits from colonial trade that were invested in real estate, luxury goods, or elsewhere, feeding the prosperity of cities like Amsterdam, Paris, Madrid, London, and Lisbon.

Two prominent urban planners in the United Kingdom, Patrick Geddes (1924) and Peter Hall (1966) , were the first to use the term world city. For them, world cities are distinctive in that they have more connections with and influence on other parts of the world. They are political centers (national capitals, capitals of an empire) and trade centers. This conceptualization examines these world cities as part of their states and identifies urban hierarchies, which are not well specified, wherein world cities are dominant. In his review of the global city debate, Acuto (2011) mentions an early debate in Chicago and McKenzie's (1927) analysis of a global network of cities. Hall (1966, p. 7) conceptualized world cities as "major centers of political power, mobility, professional talent, information and culture, as well as great centers of population that contain a significant proportion of the richest members of the community."

The emphasis on a set of cities that are central in long-distance trade and administrative/ military networks has a precedent in the field of history. Historians have identified cities that were characterized by their influence, their connections to a range of cities in different kingdoms, and the diversity of their population and economic activities (Ibn Khaldun 1986 , Abu-Lughod 1991) . Babylon, Cairo, Beijing, Samarkand, Alexandria, Carthage, and Rome are examples from the past. Sociologists and historians have explained the development of world cities in relation to the rise of trade and earlier cycles of globalization, including, in particular, finance in London (Carruthers 1999 , Cassis 2010) . Historians show that globalization processes are neither universal nor uniform but often paradoxical (Saunier & Ewen 2008) . However, they contribute to the making of urban hierarchies, namely the changing territorialization of the accumulation of wealth and power relations between cities (e.g., Subramanyam 1996 Subramanyam , 2011;; O'Rourke & Williamson 2002; Lang 2006; Hopkins 2011; Gills & Thompson 2012; Osterhammel 2014; Zinkina et al. 2019) . For instance, Darwin's (2020) analysis of port cities between 1830 and 1930 brings to light the diversity and commercial vitality of the great port cities of the nineteenth century (not only London and New York but also Buenos Aires, St. Petersburg, and Mumbai); the diversity of their populations; the large-scale recruitment of expatriate professionals (e.g., accountants); and the massive increase in food, raw materials, and manufactured goods circulating by sea. Beyond trade, cities can be centers of pandemics, fostering the circulation of viruses, or transmitters of European values. They were also centers of command and control for European states with colonial empires.

The concept of the world city was also influenced by Wallerstein's (1979) world system theory, although that theory was contested and did not attract much attention beyond sociology. Wallerstein emphasized the creation of unequal relations between centers and peripheries, namely power relations connected to capitalism. Timberlake (1985) , Chase-Dunn (1985) , and Chase-Dunn & Manning (2002) extended world system theory by looking at urban concentrations of multinational corporations and the networks connecting them. They provide rough quantitative measures to identify a hierarchical system of world cities in a world system organized by capitalism. Within this framework, world cities are centers of accumulation of wealth and power. foot_3 Connections and circulations between cities thus became the key element of the definition of the world city.

THE GLOBAL CITY AND THE INFORMATIONAL CITY: THE STRATEGIC UNIT OF ANALYSIS FOR GLOBALIZED CAPITALISM STRUCTURED BY NETWORKS

The global city was first analyzed as a political economy question to conceptualize urban worlds that, after a tumultuous decade, emerged as the new centers of the booming capitalism of the 1980s. Early debates were influenced by Marxist geographer David Harvey, whose analysis of the "spatial fix of capitalism" emphasized the crisis of accumulation and the temporal deference/spatial expansion of capitalism (Harvey 1982) . Crucially, as Arrighi (1994) argued, capitalism is the only system in history that has become global (scape and scope). The "global" in the global city debate mostly alludes to the globalization of capitalism in the early 1980s; the rescaling of the political and economic order (Brenner 1998) ; and the deep restructuring of wealth creation and economic decline in states, regions, and cities all over the world. In a world system reshaped by a new cycle of capitalism, some cities appeared as centers of wealth production and coordination. John Friedmann and Goetz Wolff, two planners based at the University of California, Los Angeles, elaborated a research agenda combining world city and global city perspectives (Friedmann & Wolff 1982) . Subsequently, Castells (1989) and Sassen (1991) published major books that structured the global city research domain.

The first round of the global city/world city debate started with Friedmann & Wolff (1982, p. 309) , who stated:

Our paper concerns the spatial articulation of the emerging world system of production and markets through a global network of cities. . . . The character of the urbanizing processes-economic, social and spatial-which defines life in these "cities" reflect, to a considerable extent, the mode of their integration into the world economy.

They raised questions about economic centers and networks, forms of city integration, and the integration of urban systems (cities) within the global system of economic relations. In order to differentiate their own view from classic views of world cities, these authors claimed, first, that the world economy has become "truly" global-whatever that means-and that the key driving force of change is international capital. Second, they developed the idea of control and command linked to the concentration of headquarters of transnational firms and banks. Third, they identified an "inherent contradiction between the interests of transnational capital and those of particular nation-states that have their own historical trajectory" (p. 312), hence the dual role of world cities. Fourth, they emphasized the conflicts and the polarization process (including racial conflicts) accompanying the process of world city formation-specifically, the gap between a permanent underclass and a class of middle-aged men who formed part of the cosmopolitan urban world and dictated the restructuring of some sections of the city to accommodate their lifestyle. For Friedmann (1995) , world cities are a class of "spatialized socio economic systems," not urban societies. Actors, organizations, and groups are not part of the framework. Friedmann's paper inaugurated the rise of numerous studies measuring connections and concentrations.

In particular, from a more sociological point of view, Alderson & Beckfield (2004) tested the world city thesis by suggesting a close connection between the fate of cities, the living conditions of their inhabitants, and the position of cities in terms of power in the world city system. They applied a rather Marxist hypothesis about globalization that suggested a reproduction of existing patterns of national inequalities in contrast to the "new" geography of globalized capitalism beyond nationstates, elaborated by Friedmann and Sassen, and the idea of the global city. They employed a narrow but rigorous methodology, acknowledging the lack of systematic data (see also Short et al. 1996) . They also provided a precise analysis of the links between multinational enterprises and their subsidiaries. That led to analyses of the power and prestige of individual cities in terms of their position within the hierarchical system of world cities. Using advanced network analysis, Alderson & Beckfield (2004) designed a telling graph of the world city system. Their analysis, within the limits of their data, is consistent with the above hypothesis. However, two decades later, one suspects that changes are occurring. These transformations are long term.

This field of research in sociology and urban studies was then profoundly transformed by two major contributions from sociologists/urban scholars. The first was Castells's (1989) conceptualization of the network society and analysis of the informational city, and the second was Sassen's (1991) theory of the global city. In both cases, the authors built a theory of certain kinds of cities and then traced its effects on a wide array of phenomena, including class structure. For Castells (1989) and Sassen (1991) , conceptualizing the informational city and the global city required them to connect territorial structures (cities) with transformations of capitalism beyond the nation-state, hence the focus on new economic sectors (information technology and finance) and the rise of networks (a radical network approach for Castells), exchanges, relations, and circulation as part of the making of a global economy. Furthermore, both authors raised sociological questions about the social urban fabric, polarization, class making, changing occupational structures, race, social segregation, and inequalities.

For many sociologists, and urban scholars more generally, the terms world city and global city are equivalent. The latter is often interpreted as more closely associated with posturing and "newness" than with substance. However, Sassen (1991) insisted on a difference between the two terms in her seminal book The Global City, among other publications. She emphasized that the concept of the global city is important in the current phase of capitalist globalization but also, in contrast to the world city literature, proposed an original sociological model, which subsequent empirical research eventually proved inaccurate. Sassen's (1991) major book has been extensively discussed (see, e.g., Robinson 2009 ). The task Sassen set for herself was difficult, and she refined her conceptualization over the years. What makes her research original is the combination of two hypotheses: one about the making of globalized networks of global cities, enabled by digital communications, and another about the rise of migration, which in turn led to the globalization of capital and labor. This combination led to the concentration of command-and-control functions of the economy in a few cities transformed by migration-a new type of city, the global city.

Sassen's argument can be considered in two ways. The first is to emphasize its analytical clarity, as her empirical research is rather straightforward. First, Sassen defines global cities as having high levels of employment in finance and producer services. Second, she ranks cities by globalness and obtains three leading cities: New York, London, and Tokyo. Third, she examines their employment and class structure, concluding that they are dual cities, due to an unusually high level of high-wage employment where workers are time scarce, leading them to require a lot of personal services that are provided by an unusually high and growing share of low-wage service workers. This situation leads to wage and spatial polarization within the metropolitan area.

However, Sassen's argument is sometimes more sophisticated while risking a lack of clarity. Sassen (1991, p. 338) concludes her book by stating that:

[C]ities play. . .a strategic role in the new form of accumulation based on finance and on the globalization of manufacturing. . . . The global city replaced the industrial/regional complex centered on the auto industry as the key engine for economic growth and social patterning. . . . The sociopolitical forms through which this new economic regime is implemented and constituted amount to a new class alignment, a new norm of consumption, where the provision of public goods and the welfare state are no longer as central as they were. . . . A focus on the actual work processes involved in these various activities reveals that it has contributed to pronounced transformations of the social structure directly through the work process in these industries-finance, producer services, and the range of industrial services they require-and indirectly through the sphere of social reproduction, the maintenance of high income and low income workers it employs. It is this combination of a new industrial complex that dominates economic growth and the sociopolitical form through which it is constituted and reproduced that is centered in major cities and contains the elements of a new type of city, the global city.

Sassen identified what she calls "parallel" transformations in New York, London, and Tokyo in terms of employment, economic structure, social relations, and interdependence between higher classes and lower classes (including migration, race issues, precariousness).

Sassen is part of a group of scholars whose work represents a major departure from classical analyses, in terms of national economies and their interdependence, in that it identifies the coherence and relative autonomy of territorialized socioeconomic systems interconnected all over the world (see also Scott 2001) . But she is also an urban sociologist and does not consider urbanization processes alone. The city (not conceived of as an independent and isolated territorial unit, of course) still makes sense as a specific territorialized social formation structured by a set of social relations and by external networks. Sassen's focus on the production side proved remarkably fruitful: Beyond the headquarters of large transnational corporations, she identified another mechanism. Dispersion of production led to the centralization of large firms and command-andcontrol techniques. These were in part outsourced to a wide range of advanced service producers (law, marketing, finance, accounting, etc.) that became concentrated in those global cities. She therefore deals with questions of employment and employment relations in the global city.

Sassen provides an important contribution to the literature on global society, going beyond an analysis of the concentration of particular social groups (upper middle classes and service professionals) and their interdependence with migrants and precarious workers who perform services for them at low wages. She also emphasizes rising migration, which became central to her later research on the sociology of globalization. The globalization of capitalism is the primary force leading to new hierarchies; different production and distribution of wealth; a new territorial order; a different social structure, including power relations, social hierarchies, and interdependence between lower-wage service workers and high-wage professionals and managers; and providers servicing the firms of the global economy. The dominant groups she identifies appear cosmopolitan and denationalized. Her focus on cities marginalizes the question of national societies and the state. She points toward polarization trends, but she identifies the mechanism leading to these trends and the making of a particular type of urban society. In the same year Sassen's book appeared, Mollenkopf & Castells (1991) published an edited volume, titled Dual City: Restructuring New York, that also put forward the idea of the strength of the social polarization process in New York.

In terms of method, Sassen was one of the few scholars at the time to develop a systematic comparison of the three global cities she identifies, though generalizing from three cases was risky-a rare intellectual move in urban research at that time (Le Galès & Robinson 2023) . For instance, clearly opposing Sassen, Abu-Lughod's (1999) book comparing three American global cities reclaimed the mantle of comparing historical trajectories without any theorizing. Sassen examined parallel transformation beyond national societies determination and suggested that, sometimes, processes of global city formation may be at play in other cities. Later, particularly in her book Cities in a World Economy (Sassen 2019) , she was less sanguine about the global city model as such. She took into account criticisms of her book on global cities to develop the idea of a transnational network of approximately 40 cities. She identified globalizing processes that affected not only the top global cities but also a wider range of cities, from Buenos Aires to Kuala Lumpur, thus undermining her own original conceptualization.

Although Castells (1989) uses a different vocabulary, that of the informational city, his thinking is related to Sassen's. After moving from Europe to Berkeley, California, Castells became a major thinker about information technologies and the transformation of societies. Famous for his analysis of spaces of flows versus spaces of places, he theorized the rise of the network society in relation to the revolution of information technology, the process of globalization, and the spreading of networking, which in his view is a new form of social organization. Like Sassen, he sees a contrast between industrial society and the informational city. He also emphasizes different trajectories of cities, moving beyond an economy-centered explanation to take into account social, cultural, political, and economic transformations. Cities have to be understood in terms of interdependence, increasingly structured by flows, circulations, and networks. In discussing these spatial processes, Castells accurately identifies the limits of the "city" vocabulary. Building on research by economic geographers, he points to the increasing significance of large urban concentrations, which he calls "metropolitan regions," characterized by intense concentrations of people, flows, activities, and infrastructures. Castells is fascinated by the rise of large Asian metropolitan regions, especially Shanghai, and with the social differentiation process associated with the rise of the informational city.

The innovative global city literature is rooted in the transformations of capitalism, unlike the classic world city literature. Both Castells and Sassen put forward a conceptualization of the global (or informational) city in contrast to the industrial city model that was in part defined by globalscale international networks and circulations. They helped explain the dualization process they identified, mostly in New York. Sassen, in particular, attempted to develop a quasi-Weberian model of the global city that articulated different dimensions but was based on three particular cases. This literature prompted empirical research examining the claims and the validity of Sassen and Castells's model.

NO GLOBAL CITIES BUT GLOBALIZING CITIES

Research about global cities, and in particular Sassen's (1991) landmark book, attracted a huge amount of attention, interest, and inevitably criticism that I cannot cover in detail in this review. Sassen triggered a wealth of empirical research either to sustain her claim about the originality of the global city model or to illustrate the combination of the trends she identified along with their singularity.

The intellectual avenue opened by Friedmann (1986) and continued by Sassen (1991) and Castells (1989) inspired a group of geographers to initiate a massive long-term empirical research program. They operationalized the concept of the global city via a ranking methodology in order to analyze and measure cities' networks and their connectivity, with an emphasis on how cities generate networks or how networks structure cities (Knox & Taylor 1995 , Taylor & Derudder 2016 ). In 1998, scholars at Loughborough University created a research network named GaWC (Globalization and World Cities) with the goal of measuring the external relations of world cities, that is, the system of relations between not only centers of government or religion but also cultural centers (Beaverstock et al. 1999 , Derudder & Taylor 2017) . They developed a sophisticated empirical analysis of world city networks (see also Smith & Timberlake 2001) , identifying a hierarchy of cities in the current global economic system. They measured all sorts of flows and gathered a wide range of indicators. Specifically, at a time when megacities were home to more than 10 million inhabitants on six continents, their results clearly separated the question of size (Lo & Yeung 1998 , Douglass 2000 , Labbé & Sorensen 2020) from that of connectivity and functions.

Megacities are not necessarily global cities, and global cities may not be megacities, as in the cases of some medium-sized European cities as well as Hong Kong, Singapore, and Dubai. The GaWC group ranked global cities mostly on the basis of economic indicators to measure their connectivity and integration into global networks. This ranking reflects pasts hierarchies and long-term unequal global relations, including colonization and the domination of American capitalism and British finance, language, institutions, and universities. It also reflects the rise of Asian economies and cities. The "winners" are the so-called alpha++ cities, namely New York and London. From the sociological point of view, this literature, however rich empirically, is characterized by the absence of theory, let alone causal theory, instead consisting of a reasonable but arbitrary statistical formula and descriptions. What is really interesting is the legitimacy and support they offered for the creation of the industry that creates indicators to rank global cities in academia and consulting (see Section 5). In his comprehensive review of the global city debate, Acuto (2011 Acuto ( , p. 2968) ) summarizes the definition of global cities/world cities in this tradition as "a social (urban) entity that 1) serves as an articulatory node of global flows; 2) performs multiple and significant world city functions; 3) contains central command roles within such functions; 4) maintains an urban order that balances aggregation and dispersion and 5) projects such order towards the global through entrepreneurial activities."

The accumulation of research led to a series of results that have now been widely shared. The first result, largely accepted, is based on work by economic geographers, urban planners, and urban sociologists: Sassen's original conceptualization does not stand up to systematic empirical scrutiny. To give Sassen her due, researchers widely recognized that some of the trends she identified, even those that were a bit sketchy (e.g., in relation to finance), were fruitful intuitions, and evidence of those trends has been found. In particular, in-depth analyses of the territorialization of capitalism by Storper (1997) and Scott (2001) brought two major points to light. First, the trend of the economy toward globalization, identified by Sassen, was underway in many territories, including cities, all over the world. Second, the relevant unit of analysis to use in understanding territorial economic restructuring is probably not the city, or only some cities, but rather the global city region: "[T]hose global city regions are the center of dense networks of transnational firms[;] they thrive on the productivity-and innovation enhancing effects of dense and multifaceted urban milieux that are simultaneously embedded in worldwide distribution networks" (Scott 2001, p. 4). Other scholars observed that the correct formulation is not simply finance capitals but, as we would say today, superstar cities. Some such cities are finance based, others tech based, still others engineering based, and so forth. This general formulation is about the places that (a) benefit from agglomeration economies, (b) attract a higher proportion of skilled workers, and (c) generate high incomes. New York, London, and Tokyo are simply a subset of this wider category.

Marcuse & van Kempen (2000) reached the same conclusion from a different perspective. They compared the effects of globalization on the internal social structure of many cities, not only global cities as defined by Sassen. Specifically, they suggested that these effects are not uniform, have long-term dynamics, are not always combined, and are strongly mediated by political processes. They contested the idea of direct translation of globalization in clear spatial patterns. Their criticism points to the lack of a precise mechanism (beyond those macroprocesses identified above) in Sassen's urban sociology.

In addition, most research has undermined the original concept of the global city because globalizing processes are at play in all kinds of cities of different sizes, including those beyond the West. Davis (2005) argued that the mechanisms through which globalization produces inequalities and segregation are visible in many cities, for instance, in Latin American cities and in Istanbul. She critiqued the narrow fixation on classic suspects (i.e., the most economically successful large cities), given that megacities are on the rise in different parts of the world. Robinson (2002) saw the global city literature as yet another attempt to promote and focus only on dominant Western cities, reflecting existing long-term power relationships, prompting the need for more cosmopolitan urban studies including "ordinary cities." Finally, measurements of financial connectivity suffer from the ignorance of less visible financial circuits. Shadow banking, illegal money circuits, and private funds are organized by other financial global cities, such as Luxembourg, Dubai, Hong Kong, and Geneva. Similarly, the global city literature tends to ignore the globalization of major organizations (e.g., mafias and gangs) that have a crucial impact on urban areas in terms of real estate investment, governance, social differentiation, and social order (Weinstein 2008 , Varese 2011 , Hazen & Rodgers 2014 , Feltran 2021) .

Similarly, the connection between the polarization thesis and globalization in Sassen's formulation has been the subject of much debate (see also Mollenkopf & Castells 1991) . However, once again, empirical research has undermined this thesis. First, while recognizing the development of social segregation at the extreme of the social structure and corresponding social segregation (in particular, self-segregation by the rich), both Hamnett (1994) , for London, and Préteceille (2016), for Paris, provided evidence contradicting Sassen's theory. Hamnett demonstrated the importance of the professionalization of the labor force under capitalism beyond globalization, which strengthened the middle classes in London. Préteceille also contested the dual-city thesis by showing that the decline of the working class goes along with professionalization and an increase in the middle and lower middle classes. Both scholars also dismissed Sassen's underdeveloped but radical view of the demise of the welfare state and the employment associated with it. In both Paris and London, the welfare state still provides a solid pillar of employment. The same is true of Tokyo and its vast middle class. No one disputes the scale of inequalities; the precariousness of some groups, which often includes migrants; or the accumulation of wealth and segregation patterns of groups at the top of the social hierarchy. However, by radically and superficially dismissing the role of the state and the welfare state [see the equally radical criticism by Therborn (2021a,b) on the illusion of global city research disconnected from the national environment and the state], Sassen's analysis of urban employment and social transformations proved either too narrow or empirically dubious. Her generalization is inaccurate for a number of cities. In many ways, Sassen's focus on a limited number of sectors was a great intuition and led to important results, but it undermined her capacity to provide a relevant analysis of the social structure of the cities she studied beyond New York.

Sassen's research also suggests a connection between the "new" social structure of global cities and the dynamics of spatial segregation, together with the distinct polarization of global cities. Few sociologists have taken up the challenge of articulating globalization, class making, and patterns of social segregation at different scales (Sklair 2001, Savage et al. 2004 , Savage 2021) . A group of scholars examined Sassen's thesis more precisely, 30 years later, in New York, London, and Paris (Van Ham et al. 2020 , 2021) . Their research confirms the rise and concentration of high-wage jobs in these three cities, as Préteceille (1995) and Hamnett (1994 Hamnett ( , 2021) ) had shown, along with a decline in low-wage jobs. They find patterns of social segregation that are common in many cities all over the world, namely (a) gentrification in the city center, (b) displacement of low-wage jobs and poverty to the periphery, and (c) an increase in segregation, leading to what they call the "global segregation thesis." In other words, cities might be globalizing, but processes of segregation in socalled global cities are widely found around the world. There is no evidence of clear polarization, not even in Hong Kong (Chiu & Lui 2004) .

In contrast to Sassen's argument signaling common trends toward polarization in three global cities, many scholars have argued that Tokyo does not fit the global city category in important ways (Hill & Kim 2000 , Sorensen 2003) . Similarly, in his sociological analysis of the effect of globalization of Latin American cities, Roberts (2005) identifies far more contradictions than convergence. Van Ham et al. (2020 , 2021) emphasize the contrast between the unusually high segregation rate in New York and the lower rate in Tokyo. One of their most interesting findings is related to the time dimension of social segregation processes. In many ways, the rise in inequality has not been clearly expressed in terms of segregation and separation. However, they convincingly argue that it takes time before higher inequality or changing occupation patterns are translated in terms of social segregation. Specifically, the so-called segregation paradox identified in some cities (i.e., the decline in income segregation at a time of increased income inequality) may simply disappear over time. In other words, these authors predict a continued increase in social segregation in many cities all over the world.

In the case of Paris, Godechot (2013) used precise individual-level data to show the mechanisms by which global cities contribute to inequality. Among the advanced service producers identified by Sassen, finance is a major mechanism, and there is now a robust literature about the financialization of capitalism. Sociologists and economists have noted the scale of income earned by top finance professionals, suggesting a massive contribution to the creation of inequalities. Reframing Sassen's hypothesis in relation to finance, Godechot documents the concentration of the finance sector in global cities as defined by Sassen. Usually, most quantitative studies on inequalities are firmly inscribed in a national framework. As part of a major international comparative research project drawing on Krippner's (2011) classic analysis of financialization, Godechot incorporated results about the importance of not only financial employment but also, more starkly, the distribution of profits. Godechot (2013, p. viii) studied not only average wages in finance but also the "highest end of the spectrum." As a result of what he calls the "financialization of finance," there is a huge disparity between the wages earned by the top 1% and 0.1% of those working in finance (either in the financial sector or not) and everyone else. In support of Sassen's thesis, Godechot showed that the top earners in finance were concentrated in the Paris Île de France urban region (i.e., the most globalized French city) and that they contributed massively to inequality. Specifically, the rise in wage inequality in France arises mostly from this urban region and two-thirds of the increase in inequality within this area is explained by the increase in top wages within the financial sector.

Regarding segregation, Godechot (2013) uses a different data set to show that the level of residential segregation is more important in Paris Île de France than elsewhere but that it has increased only slightly over the past 50 years, not on the scale envisaged by Sassen. This increase is, as argued by Préteceille (1995) , explained mostly by the self-segregation of the superrich. Godechot (2013, p. xxxi) concludes, in contrast to Sassen or Castells, that for Paris "it is primarily financialization, rather than globalization, that is leading to the increased domination of the major megacities." However, separating the two is not simple, as the growth of the financial industry is connected to forms of globalization, such as the information technology revolution, that reduced the cost of moving capital or the spreading of policies toward convertible currencies.

These results for Paris were then tested in 30 Western cities by a large group of researchers (Godechot et al. 2023 ) using public employer-employee data from 10 countries. Financialization, far more than globalization, constitutes the major contribution of global cities to the production of inequality, because the concentration of high-paying jobs is primarily in finance. Godechot et al. demonstrate the increasing importance of the financial city in local earnings inequalities. As one would expect, the gap is more pronounced in high-inequality countries like the United States than in lower-inequality countries such as those in Northern Europe. Global cities concentrate the top 1% of earners and are more unequal. Therefore, they "show that global financial cities are significant geographical sites in which inequality is shaped" (Godechot et al. 2023, p. 19) .

Empirical research conducted after the publication of Sassen's (1991) book has convincingly shown the limits of Sassen's theory for a particular subset of large, economically dynamic cities. In contrast to the originality of the global city model, researchers have emphasized that the dynamics of globalization triggers social and spatial changes in many cities. This displacement toward globalizing cities suggests that the largest megapolises are distinctive because of the scale of their infrastructure and planning but are not as relevant in terms of sociology (Labbé & Sorensen 2020). Many researchers instead use the term superstar city to suggest that there is no such thing as a global city as an original sociological model. Some trends identified by Sassen and Castells are taking place in many different-sized cities all around the world, and some of these cities tend to aggregate certain groups and activities. Their economic performance is outstanding not only because of finance but also because of high tech, services, the concentration of skilled labor, financial and human flows, and the scale of inequality.

IMAGINING GLOBAL CITIES

Most of the above discussion of global cities is concerned with globalization, explained by the transformation of capitalism beyond the nation-state, the rise of flows of capital, people, information, ideas, and polarization within cities. As mentioned in Section 1, by contrast, historians of world cities have empirically emphasized different dimensions of the world city-making process. 3 Beyond wealth, agglomeration, skills, and trade, research on world cities or global cities has been concerned with the social and cultural diversity of residents and visitors and with the imagination developed around those cities.

This research raises classic sociological questions: To what extent are urban societies in global/world/alpha/superstar or globalizing cities different from national societies or from other cities or territories, and what sorts of urban societies are those global cities creating? Do globalizing cities contribute to the making of different societies and urban lives? Using Bourdieu's conceptual apparatus, Savage (2017) conceptualized the "metropolitan habitus." Butler & Robson (2003) used this concept to investigate the role of London's middle classes in school choice, as actors of gentrification, in their obsession about social reproduction, and in searching for a particular aesthetic. Cities continue to be sites of elite accumulation of capital and for the generation of capital from past investments. Savage (2017) documents the making of social capital (i.e., the number of weak ties), cultural capital, and economic capital in large UK cities. He argues that cultural capital is less oriented toward the national society and more toward the cultural capital generated in other global or globalizing cities. He therefore identifies "urban elite cosmopolitanism" and historical relations of domination within cities that are increasingly dominated by those elites and their reproduction strategies. Therefore, global cities are also defined according to their aesthetic qualities, the high culture that defines elites' preference. This line of inquiry is promising and would require systematic comparative research that has not yet been performed.

The differentiation of urban societies in global cities within national or global societies remains a major area of research. The sociological literature has not produced systematic comparative results, and recent analyses have undermined the concept of the global city. However, the sociological literature has contributed to this debate with stimulating insights, often disconnected from one another. This section reviews these insights in terms of circulation and socioethnic diversity; concentration of the superrich; and renewed imagination about urban futures, including the climate crisis.

Global Cities as Hyperdiverse and Cosmopolitan Cities?

Historically, the city has been defined in part by the arrival of migrants; by the uncertainty created by the existence of foreigners; and by invisible, sometimes ungoverned activities. As mentioned above, from the point of view of migration, the large-scale transnational migration taking place today is similar to what occurred at the end of the nineteenth century and prior to World War I. Even if this is a case of globalizing cities (i.e., migrants becoming more present in all sorts of cities), some cities are concentrating very high proportions of migrants. The description of urban societies in terms of hyperpluralism, or cosmopolitanism, simply sketches their characteristics in world cities/globalizing cities.

For instance, King (2004 King ( , 2015) ) strongly influenced the organization of the global city debate around migrations, urbanism, and most importantly the historical trajectories and circulations explained by colonization. His research on imperial London emphasizes the imperial legacy and the diversity within the population, explained by colonization and capitalist globalization. He criticized the narrow Marxist economic conception of global cities and scholars' ignorance of cities outside the West. Much global city research has been conducted in migrant cities, or places of arrival for all sorts of migrants and hubs of transnational migration and urbanism (Smith 2001) . Migrants contribute significantly to the weaving of the urban fabric, and diverse migrant communities contribute to the globalization of mosaic cities. Transnational diasporas (Eade et al. 2002) , for instance, bring a particular dynamic to the making of different social worlds, cultures, religions, food, and social dynamics in these cities. Increased flows of migration trigger the rise of globalizing cities.

Over time, some cities have come to specialize as gateway cities for migrants, a good indicator of globalizing cities (Price & Benton-Short 2008 , Glick Schiller & Çaglar 2011 , Farrer 2019) . The contested term "superdiversity," proposed by Vertovec (2023) , suggests that some cities (e.g., Toronto, Copenhagen, New York) are now characterized by a high proportion of foreign-born populations, leading to urban processes of linguistic, cultural, religious, and social diversification. In this perspective, multiple social processes of differentiation and increasing social complexity are the norm. Using United Nations data, Price (2017) identified twentieth-century gateway cities-New York as well as Chicago and Los Angeles in the United States (Abu-Lughod 1999) in addition to London, Buenos Aires, and Hong Kong. More recently, these cities were joined by Toronto, Copenhagen, Abu Dhabi, Dubai, Doha, Dublin, Houston, Singapore, Seoul, Santiago, and Shanghai. According to Price (2017) , each of these cities, along with Madrid, Sydney, Johannesburg, Kuwait City, and Paris, has a foreign population of more than one million people. By contrast, some megacities, such as Tokyo, are still characterized by a very low level of international migration. In some Middle Eastern cities, such as Dubai, the national population makes up only around 8% of the overall population, creating a social fabric made of rich local populations, large populations of precarious migrants from Asia who live in camps on the outskirts, and a large body of expatriates (Kathiravelu 2016, Le Renard 2021). The globalizing characteristic of such cities is related not to their size but rather to their capacity to attract expatriates (both rich and poor), projects, visitors, and flows of capital.

These cities are also characterized by the mobility of different groups, from migrants to global elites to diasporas. In many cases they constitute transnational spaces, which contribute to the territorialization of transnational networks (Hannerz 1996) . This phenomenon is not new historically and is not limited to global cities, but its concentration in some cities might lead toward either greater intensity or a different type of urban society. Comparative studies in this area are still limited, and much empirical research is required in order to generalize.

Global Cities as Safes and as a Playing Field for the Global Rich?

In the economic development model of the global city, the global city is increasingly measured by its capacity to attract the superrich or superbourgeoisie (Robinson & Harris 2000) . That attribute is not completely new in history, but the globalization of the phenomenon is on a different scale. According to the 2023 wealth report produced by Swiss bank UBS, foot_10 the world contains just under 60 million millionaires (mostly in the United States and China) and more than 3,000 billionaires. Cousin & Chauvin (2021, p. 2) define the superbourgeoisie in terms of its "unequaled level of wealth and global interconnectedness, its transnational ubiquity and concentration in the planet's major cities, its specific culture, sites of sociability and shared preference, and even by class consciousness and capacity to act collectively." In relation to globalized capitalism, Sklair (2001) theorized the making of a capitalist transnational class whose priorities and needs are central for the reshaping of many cities, including in terms of architecture and iconic buildings (Sklair 2005). In less sociological terms, the ultrahigh-net-worth individual (i.e., an individual with a net worth greater than $30 million) has become a standard category for consultants, marketing executives, and policy makers, another example of category creation. These individuals live mostly in New York, Los Angeles, London, Shanghai, Hong Kong, Singapore, or Beijing, but cities of the Middle East are catching up. Cities with large proportions of millionaires also include Moscow, Tokyo, Delhi, Mumbai, Sydney, São Paulo, Istanbul, Jakarta, and Bangkok.

Researchers have identified urban transformations in globalizing cities/world cities put forward by private developers and the finance sector to accommodate and attract wealthy families, the upper middle classes, and tourists, such as the development of consumption centers (luxury shopping malls), museified traditional neighborhoods, cultural centers and museums located in buildings designed by star architects, or urban renewal organized by megaprojects (Fainstein 2008) or triggered by global events such as the Olympic Games or world exhibitions. Knowles (2022) argues that some cities have become "plutocrat paradises" and, to some extent, captured by the super wealthy (Forrest et al. 2017 , Atkinson 2020) . Rich transnational migrants are moving to global cities in order to access the most famous restaurants (Farrer 2015) , the most exclusive shops, and the most exclusive services. For instance, Liu-Farrer (2016) provides a vivid account of wealthy Chinese families moving to Tokyo. She shows how the move to what is perceived as a global city is a strategy to secure social status and join the global elites. Elite urban neighborhoods and expensive real estate have been developed in cities all over the world, ranging from Lagos to Jakarta, from São Paulo to Luanda, from Cairo to Bangkok.

Global cities have attracted massive investments as safe cities where wealthy families can park their money in real estate. Many real estate projects have been developed in order to feed this urban boosterism without much consideration for the existing inhabitants. Global cities (i.e., globalizing cities) are thus also defined by real estate investments and by the making of spectacular urban projects for the rich that lead to ever-increasing costs of housing (Bishop et al. 2013 , Le Galès & Pierson 2019) . They are characterized not only by the concentration of particular professionals but also as a playing field for global wealthy elites. In London or Dubai, as in many other globalizing cities, the financialization of housing and real estate is the result of the intensity of urbanization, a decade of cheap abundant money (Aalbers 2016), and real estate investments by family offices. Massive amounts of money have been invested in real estate in the most prestigious cities, which combine few regulations with abundant consumption opportunities and high-end culture.

Wealthy elites shape global cities in their image, creating a world of gated communities, gentrification, and luxury developments. Indeed, similar to New York, London, or Los Angeles, cities like Singapore, Hong Kong, Dubai, and the planned city Neom in Saudi Arabia are now engaged in a fierce competition to attract wealthy families and their investments.

Global City Imagination

As is clear from this review, the relative failure of the global city project in sociology has been inversely proportional to its spectacular success in public debates around the world. The global city has attracted massive attention, leading to the rise of an industry that aims to characterize, measure, and especially rank global cities. Consultants working for business interests, science fiction writers, empirical geographers, and others have put forward representations, definitions, and imaginings of what a global city might be. This section describes what a sociology of the global city might be in terms of images, representations, ideas, and measures.

First, the sociology of the global city could become a sociology of urban imaginaries fed by art and artists, such as the novels of Italo Calvino, dystopic science fiction, and increasingly art about climate catastrophe. Perceptions, images, information, and the senses are increasingly becoming part of this sociology of the global city. It is regarded in terms of articulation of many world cultures (Huyssen 2008) . Interestingly, such cities are emerging beyond the Western world: Mexico City, Rio de Janeiro, Lagos, Kinshasa, Bangkok, Dubai, Shanghai, and Lima, for instance.

Second, the global city imagination has taken a normative stance. Japanese sociologist Machimura (2019) has suggested that the world city/global city conceptualization debate has been marginalized in favor of "the world city as a traveling policy" to enhance economic competition. The public imagination of global cities, in particular for media and policy makers and a range of business interests, has been shaped by economic indicators and rankings of global cities. The sociology of global cities has become the sociology of the competition between those cities and their leaders to appear, to be recognized, and to project themselves as global cities; the result is a massive increase in marketing investment to "raise the profile" of many cities. Classic results from the sociology of ranking (e.g., of universities; Espeland & Sauder 2007), including mechanisms of self-fulfilling prophecy and commensuration, can help us make sense of these ranking activities. In addition to the GaWC group's measuring and ranking activities, several consultants and think tanks have produced their own global city rankings. 5 Various networks of cities have also promoted their indicators of globalization.

Research in different world cities has connected what Harvey (1989) famously analyzed as the "entrepreneurial urban governance of cities" with globalization. In many cities, "urban growth machines," to use the classic concept proposed by Logan & Molotch (2007) , have emerged to promote each city as a global city, mostly to open it for business and to attract flows of capital, wealthy families and the upper middle classes, cultural investments by transnational corporations or foundations (e.g., Guggenheim, Disney), and global events (e.g., sporting events, world exhibitions, high-tech conferences, music festivals, video game competitions). Such promotion justifies tax cuts for those upper classes, designated by the word "talent"; tax exemptions for the private investors in these activities; work for myriad specialized consultants; construction of more iconic buildings and modernist infrastructure such as mega-airports, business districts, and luxury shopping malls; and more displacement of populations from high-value urban spaces. These developments have been spectacular in terms of speed and scale in rapidly developing cities in Asia, in oil-rich cities in the Middle East, and increasingly in booming African cities such as Lagos.

In their edited volume titled Worlding Cities: Asian Experiments and the Art of Being Global, Roy & Ong (2011) apply a critical hyperconstructivist anthropology/planning perspective to insightfully analyze investments by national elites in promotion of their cities as global. Cities are being reshaped in relation to the set of norms and designs that are represented as those of a great global city. For instance, the literature has documented the rise of star global architects and investments in iconic buildings and design to symbolize the power and prestige of particular cities. In most cases, these developments took place without much concern for citizens; democracy is usually not in the cards (Guggenheim & Söderström 2009 , McNeill 2009 , Ponzini 2011 , Ponzini & Nastasi 2011) . In this sense, the global city can be analyzed in terms of the "fictitious expectations" that Beckert (2016) conceptualized to understand capitalism. Ong (2011, p. 11 ) defines worlding as "identify[ing] the projects and practices that instantiate some vision of the world in formation." Although these scholars dispute the existence of a world city model, they identify many of them. They see not one model of the global city but rather three "ways of being global," particularly the imitation of models of future global cities based on iconic buildings, cultural districts, and corporate headquarters (very visible in, e.g., Hong Kong's self-promotion as an "Asia world city"). They also identify a model based on new solidarities and another one about interreferences. The first has become a norm: Scholars have studied the strategies developed by the elite to invent, mimic, or simply feel obligated to make their city appear to be a global city.

For instance, Acuto (2022), Singerman & Amar (2009), and Molotch & Ponzini (2019) show the power of this type of imagination in the "building global city" strategy of Middle East elites. World city-making strategies in Delhi have also revealed the strength of this global city imagination (Dupont 2011 ): Implementation of this strategy comprised aesthetic governmentality, criminalization of the poor, and promotion of cultural centers (Ghertner 2015) . In sociological terms, such developments are often studied either with the tools of anthropology and cultural sociology, as in studies of religion (Garbin & Strhan 2017), or, more often, in terms of the sociology of science and technology. An increasing number of sociologists and geographers are using pragmatic research from science and technology studies to emphasize the multiplicity of processes, objects, material infrastructure, and discourses that are assembling the city in many different ways, (Farías & Bender 2012) . That allows scholars to bring together imaginations, material dispositifs, and networks in ever-changing configurations and to reject the idea of the city as whole, however globalized it might be. Andreotti et al. (2015) have also studied this imagination of global cities and globalization. In their comparative research on upper-middle-class mobility in European cities, these authors show that, even when they are not transnationally mobile and are deeply rooted in their city, those middle classes have a strong "globalized mind." Theorists of mobility also point to global cities as a natural landing point for these middle classes (e.g., Elliott & Urry 2010) .

The global city/world city question is also an opportunity to examine some forms of global culture in the making, beyond consumerism, global trademarks, or the rationalization/ McDonaldization thesis (Ritzer 1996) . The representation of a world of cities has been fostered by measures, comparison, and competition between cities. Such competition often combines imitation processes (e.g., a new opera, the organization of the World Cup) and differentiation processes. In order to attract tourists (one measure suggests that there were 1.2 billion international tourists in 2022; Statista Res. Dep. 2024) , city elites attempt to differentiate themselves in terms of culture, food, architecture, innovation, and history ( Judd & Fainstein 1999 , Olds 2002) . Migration is also essential, and scholars have developed measures about the scale of migration in various cities and their ranking (Benton-Short et al. 2005) .

Various market research companies produce rankings of cities, chosen by international tourists, that usually yield a handful of European cities, led by Paris, but also places such as Dubai and Mexico City; Asian cities such as Beijing, Singapore, and Hong Kong; and American cities such as New York, San Francisco, and Orlando. Beyond tourism, the imagination of globalization and global cities also penetrates the mind of a social group. Andreotti et al. (2015) show that many members of this social group are not internationally mobile and have deep social roots in their city. However, they distinguish themselves from the rest of their society by their "globalized minds" and references to global cities.

The anthropology of food has also produced stimulating contributions to globalization processes, including the making of world cities. Farrer's (2015) analysis of the globalization of Asian food, which he calls "culinary globalization," is a fascinating example of this articulation of cultural 662 Le Galès globalization processes, networks, circulations, and cities which underscores the mix of territorialization, deterritorialization, invention of local traditions, and hybridization that is particularly salient in many cities. In this sense, world cities are those where such processes are especially diverse and intense (i.e., the diversification of food, architecture, and culture; Ren 2011).

Taking into account different debates about global cities, Cousin & Chauvin (2021, p. 5) bravely attempt to characterize the global city as "the combination of economic dynamism, bustling cultural life, political liberalism, market base regulation and fast growing real estate valuation." One might add certain violent forms of exclusion (Kruijt & Koonings 2009) , social movements, violence, and inequalities (Madden 2012) . These elements also include institutions of sociability (e.g., clubs) or leading universities and business schools (Chakravarty et al. 2021) . While this combination of elements may be found in many globalizing cities, they are especially concentrated in superstar cities and are widespread in many globalizing cities.

CONCLUSION

This review has analyzed the rise and fall of the sociology of the global city since Sassen's (1991) innovative book, which inaugurated an important field of research and found great success among urban, media, economic, and political elites. This review has framed the global city debate so as to take into account the legacy of world city research led by historians and sociological research about globalizing cities. Sassen was among the first to identify particular transformations occurring within some cities (Robinson 2009) . The sociology of global cities has been one element of the making of a global urban sociology (Garrido et al. 2021 ). However, this review argues that comparative empirical research undermined this exciting intellectual project and that the conceptualization of the global city was abandoned by urban scholars and sociologists alike. Even prominent urban planners and geographers who kept the flame of the debate about global cities alive have now moved on to analyzing globalizing cities (Brenner 1998 , Ren & Keil 2017) . The ambitious sociological model of global cities did not survive empirical examination. However, it contributed to our understanding of the mechanisms connecting globalization processes and spatial forms. It proposed the role of circulation and connection in the making of the unequal world of globalizing large metropolises.

The question of the global city is also contested because of issues raised by various political events and doubts about globalization in different parts of the world. For instance, Machimura (1992 Machimura ( , 1998 Machimura ( , 2019)) , once a subtle analyst of the globalization of Tokyo, now writes about the deglobalization of Tokyo, and Douglass (2009) is sketching alternatives to the global city model of Southeast Asia. After all, the world may soon reach the peak of urbanization and globalization. Furthermore, the COVID-19 pandemic (Ali et al. 2022) , the rise of protectionism, and capitalist globalization that seems to be running out of steam may accelerate the decline in significance of the global city concept.

FUTURE ISSUES

Two issues might be considered for future research. The first is an important and unsolved question in the literature: Is there something special about megacities (i.e., cities with 10 million or more residents), globalizing cities, superstar cities, or particular types of cities in connection to the global? There is confusion about this issue, in that it "feels" like there is something different (in Simmel's sense), but we cannot detect it in data such as incomes or education. Research has already shown how social movements have contributed to the making of the global city (Keil 1998 , Hamel et al. 2003) . As Savage (2017 Savage ( , 2021) ) has shown, people living in a certain type of city tend to be more culturally oriented toward global culture or to have nonnational networks. Is it possible to identify more precisely some form of cosmopolitanism in globalized cities (Beck 2007 (Beck , 2018) ) or some form of urban cosmopolitics (Blok & Farías 2016)? Also, is it possible to document different uses of space or forms of urbanity (Gans 2002 , Zukin et al. 2015) ? Addressing these questions requires far more comparative empirical research in different contexts.

More comparative research needs to be done on the differentiation between leading global cities producing wealth and the concentration of educated upper middle classes versus other territories. Also, from a political sociological point of view, the global city debate has often ignored the agency of groups and actors able to produce collective action in cities (i.e., the governance question). By contrast, Acuto (2013) and Oosterlynck et al. (2019) have studied the global city as a global political actor, adding particular political connections between cities as an important dimension of policy transfer and global city making, including informalization of the state (Boudreau 2016). Questions of the political differentiation of some types of cities in relation to the state or national society may help us conceptualize globalizing cities in a more Weberian perspective, for instance, in terms of quasi-city-states attracting visitors and migrants, symbolic projects, experts, and capital (Therborn 2021a).

The second future issue is that the climate crisis has become the new global horizon for globalizing and global cities that will be especially affected by floods (many such cities are coastal); air pollution; pandemics; migration; waste; and access to water, energy, and food. The globalizing city research agenda is increasingly being determined by the climate crisis and the environmental transition (Bulkeley & Castán Broto 2013 , Bravo 2018) . Superstar cities or global cities are also major centers of pollution, waste, carbon emissions, and consumption of energy and water. Rose & Fitzgerald (2022) have developed a radical and innovative research agenda about the urban brain and mental health of city residents. An area of research is devoted to epigenetics or to connecting conditions of urban life with mental and physical health issues (Winz & Söderström 2021) . Addressing these questions about differentiated urban societies in globalizing cities requires not only more theory but also innovative comparative methods articulating different scales and measures of mobility, as suggested by Sampson & Candipan (2023) in their comparison of US neighborhoods and cities.

DISCLOSURE STATEMENT

The author is not aware of any affiliations, memberships, funding, or financial holdings that might be perceived as affecting the objectivity of this review.

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