INTRODUCTION

Since the 1980s, scholars have studied the different notions of frontier in Argentina. Although this concept was traditionally associated with national states, recent academic production has related it to other processes and forms of appropriation and use of the physical space, such as ethnic differences, population mobility, exclusion, social inequality, or the construction of identities and alterities. The associations among actors from different hierarchies at different spatial and temporal scales have also been discussed.

These academic studies (from different fields) can be classified into four main lines of research associated with the different types of frontier: interethnic, interstate (national), production, and urban/periurban frontiers. This classification is based on a proposal by ^{Benedetti and Salizzi (2014)} , who examined interethnic, interstate, and production frontiers (the latter are fundamentally agrarian) in connection with the construction process of the Argentinian territory. While these three types of frontiers are associated with national and regional scales (more or less stable over time), this review includes other types of frontiers, at smaller scales, which explain numerous forms of spatial discontinuity expressed in everyday life, for example, frontiers within cities or transitional spaces between rural and urban environments. Each of these four lines was built based on contributions from different disciplines, and they emerged and consolidated themselves at different times.

Thus, via different research trajectories, the interest in the academic study of frontiers in Argentina contributed to the formation of a field of study. When we point out the existence of a field of study, we refer to a system of relationships among different stances built around this “knowledge” (Bordieu, in ^{Benedetti, 2017a} ), which becomes visible in the form of academic production.

In this regard, the transdisciplinary strategies that social studies are increasingly adopting to develop integral approaches to certain problems highlight the necessity of avoiding individual disciplinary perspectives to outline and construct objects of study concerning complex fields of knowledge structured around social life phenomena.

The present study sought to systematize the academic production developed in Argentina⁶ associated with the aforementioned lines of inquiry. To this end, we present a state of the art review comprising a group of studies on local referents that laid the foundations for the consolidation of the research trajectories and represent a highly relevant background for future research. The starting point of the present study was the 1980s and the return to democracy, which, as can be appreciated from the literature review, marks the beginning of the vast majority of current research lines. This article is mainly descriptive due to the large number of bibliographic references included, but also because our purpose was to propose a systematic view of the national academic discourse structured around the concept of frontier in Argentina. Our proposal is intended as a contemporary approach including a wide range of associated notions (e.g., strips, limits, borders, fronts interfaces, walls, etc.), as well as their respective interrelationships.

This study represents part of a collective research project carried out by the Study Group on Borders and Regions (GEFRE) of the University of Buenos Aires⁷ with the purpose of creating an interdisciplinary space for academic research and training centered on the concept of frontier and its multiple meanings.⁸

The paper was structured in four sections based on the types of frontier addressed by the literature (interethnic, agrarian, interstate, and urban/peri-urban). The present study examines the categories used in the different studies, their central axes of analysis, the main authors who have contributed the field, as well as specific considerations. Finally, we reflect on the general characteristics of the field of frontier studies in Argentina.

INTERETHNIC BORDERS

Interethnic borders refer to a series of spatio-temporal entities present in the Argentinian context since the colonization of the South American subcontinent to the present.⁹ In general terms, they are the expression of contact, interaction, and conquer processes involving groups of unequal political, cultural, or economic structures. In South America, these processes unfolded historically as: a) the successive advances of the Iberian colonial society over the territories controlled by indigenous groups between the sixteenth and the early nineteenth centuries, and b) the expansion processes of national states over territories in control of indigenous peoples that had not yet been subjugated since the nineteenth century onward. Even today, these entities refer to instances of reproduction of ethnic differences expressed in the territory as some type of border.

Three major moments, associated with the emergence of different interethnic frontiers, can be recognized in the current configuration of the Argentinian territory. Two frontiers were formed in the first decades of the nineteenth century.

One of them has often been the focus of academic research, and authors have referred to it using different terms: ‘the southern border’ ( ^{Navarro Floria, 2001} ; ^{de Jong, 2016} ), ‘the Pampean border’ ( ^{Mayo, 2000} ), ‘the Buenos Aires border’ ( ^{Duart, 2000} ; ^{Banzato, 2009} ), ‘the southern border of the Buenos Aires province’ ( ^{Ratto, 2003} ), ‘the Cordobese southern border’ ( ^{Tamagnini & Pérez Zavala, 2013} ), and ‘southern Argentinian border’ ( ^{Quijada, 2002} ). This territory extends from the Atlantic to the Pacific Ocean, and its boundaries responded to spatial and cultural practices; this border maintained a certain degree of functional continuity between the sixteenth and nineteenth centuries, until the creation of the Argentinian State ( ^{de Jong, 2016} ).

The regions known as Araucanía, Pampa, and Patagonia were located south of the conquered territories. Rather than a line of demarcation, this border was transitional region between Spanish-Creole and indigenous societies, where war, diplomatic tension, violence, and sporadic moments of peace followed one another ( ^{Tamagnini & Pérez Zavala, 2016} ). The critical study of this frontier region was initiated, for the most part, by the fields of historical research ( ^{Mandrini, 1992} , ²⁰¹³⁾ and historical anthropology; its theoretical and methodological approaches are currently under discussion ( ^{de Jong, 2016} ).

The other interethnic border is located close to the Gran Chaco region, and it has been called ‘the northern border’ ( ^{Spota, 2010} ) and ‘the Chaco border’ ( ^{Teruel, 2005} ). ^{Cruz (2014)} described its conformation during the colonial period in the proximity of the cities of Jujuy and Tucumán and emphasized that this area was the entry point to the Chaco for expeditions aimed at enslaving local population. ^{Teruel (2003} , ²⁰⁰⁵⁾ analyzed colonization movements from Salta in this context. Other authors, for instance ^{Lucaioli (2010)} , focused their attention on the eastern sector: the north of the Santa Fe Province.

The terms southern border and northern border denote a certain inherent geographical positioning; its epistemological correlate emphasizes that the perspective is centered on Buenos Aires. However, the intent of the aforementioned studies was to add complexity to the study of interethnic frontiers by challenging their binary interpretation as a line separating “civilization” from “barbarity.”

In these new perspectives, frontiers are environments in which social groups with diverse and contradictory interests come into contact in a dynamic and changing historical process ( ^{Nacuzzi & Lucaioli, 2014} ). These groups of studies are divided into two different research lines depending on the specific border that they study; scholars tend to study the borders located near the cities where they are based. Thus, the northern border of Argentina is usually studied by academics who live in the northern provinces of Jujuy and Salta. A cross-sectional perspective reveals the absence of systematic comparisons and studies involving both borders (north and south), except for the studies by ^{Nacuzzi (2007)} , ^{Ratto (2011)} , and ^{Nacuzzi and Lucaioli (2014)} .

A massive incorporation of land into the Argentinian territory took place between the 1860s and the 1900s in the south and the 1930s in the north. The cornering, subjugation, and extermination of indigenous groups followed, and these borders were deactivated; to this day, they are still presented as internal boundaries ( ^{Duart, 2000} ). The historical episode that decisively contributed to the blurring of the southern border was termed ‘Campaign of the Desert’ by traditional historiography. ^{Escolar, Tarquini, and Vezub (2015)} conducted an extensive review of this military enterprise, which they described as the main event of the military epic of the national formation process, the acquisition of its territory, and the conformation of the modern Argentinian population.

The occupation of the southern part of the Gran Chaco is usually considered to have occurred after 1884, when a military campaign (similar to the southern military campaign) was initiated, although ^{Spota (2010)} suggests that the process was already underway since the so-called War of the Triple Alliance (1864-1870). The border was not fully eliminated until the 1930s, with the episode known as the Pacification of the Chaco.

At present, some studies continue to use the concept of frontier to account for the relationships between society in general and indigenous minorities or for the advance of capitalism in certain sectors of the country. ^{Gordillo and Leguizamón (2002)} analyzed different processes around the end of the twentieth century and highlighted the close relationship between the border and violence. On the other hand, with an eye toward the present, ^{Trinchero (2000)} proposed the concept of social formation of frontiers to account for the processes of cornering, subjection, and submission of labor to capital. The border is understood as a process of connection between spaces characterized by heterogeneous production and reproduction dynamics—it is no longer seen as a point of contact and becomes an environment of changing and flexible configurations.

AGRICULTURAL FRONTIERS

The process of allocating new lands to agricultural and stockbreeding activities in Argentina has been referred to using a wide range of terms (‘pioneer strip’, ‘colonization front’, ‘pioneer front’, ‘agricultural frontier’, ‘agricultural and livestock border’); they are used interchangeably to minimize the attention paid to their specific meanings. This topic has been analyzed from different perspectives and by different disciplines; they have revealed a renewed thrust toward development, reflected by the expansion of the production model of agribusiness in the region.

A number of noteworthy geographical studies define the agricultural frontier as their object of study and analyze its special characteristics based on different dimensions. Other disciplinary fields tend to define the agrarian frontier in terms of production or as a result of the consequences of agribusiness expansion. In the second case, the frontier is treated more as a piece of information or a general context than as an object of study; therefore, it is entangled with the agribusiness expansion process and its potential as an analytic tool is lost.

The study of agrarian frontiers gained notoriety in the academic agenda only at the end of the 1970s. Until then, the relevant concepts and notions had been addressed superficially, and the discussion had been limited to the study of the process of conformation of the national hinterland ( ^{Giberti, 1970} ; ^{Denis, 1987} ; ^{Gaignard, 1989} ). The geographical studies conducted by ^{Reboratti (1979} ; ¹⁹⁸⁹ ; ¹⁹⁹⁰⁾ were of utmost importance to the renovation of the field and the consolidation of its own thematic scope. ^{Reboratti (1979)} analyzed the occupation of new lands in the Alto Paraná-Uruguay basin (Misiones Province) with the purpose of establishing a typology of the mechanisms of advancement of the border and their interrelationships with population processes.

Although this proposal was embedded in classical studies on pioneer fronts, influenced by the contributions of French and Brazilian geographers, its approach was characterized by a constant concern about the conceptual content of the agrarian frontier. This line of work was further deepened by the study of the Umbral al Chaco region, also in northern Argentina ( ^{Reboratti, 1989} ), and was reflected in a study focused entirely on agrarian frontiers in South America ( ^{Reboratti, 1990} ), where the author compiled and organized previous reflections.

Toward the end of the twentieth century, the study of agrarian frontiers focused on the expansion of agrarian capital and the transformation of production practices and agrarian structures. At this point, it becomes clear that the approach has been focused on the different moments experienced by the country as the agro-industrial production model was being introduced. Before 1990, when the process was still in its infancy, studies reproduced classic approaches. Since then, in response to the so-called “agrarization” and “sojization” of agricultural activities (transformation of natural or semi-natural ecosystems into agrosystems and soybean as a monoculture), the discussion moved progressively away from population issues to the reorganization of the production space and its effects.

These studies can be systematized based on the type of theoretical-conceptual analyses that they perform. We identified a series of studies that address the concept of frontier, but its scope is not theoretically discussed. These studies focus mainly on the consequences of the expansion of agribusiness. The agrarian frontier is not their object of study, and its special characteristics are not part of the discussion. Examples of this group of studies from the field of technical agronomic studies usually refer to the agrarian frontier as a mere extension of the area devoted to a certain production activity (see ^{Agostini & Giunta, 1987} ). The productivist point of view of these studies confines their attention to the assessment of the physical capacities of certain spaces to accommodate more cultivated lands in order to guarantee Argentina’s insertion into the global commodity market.

Another series of contributions seek to differentiate themselves from this vision and focus on the study of the damage caused by agricultural and stockbreeding expansion. Two groups can be differentiated. The first group includes environmental analyses of the consequences of such expansion ( ^{Cabido, Zak, Cingolandi, Cáceres, & Díaz, 2005} ; ^{Viglizzo & Jobbágy, 2010} ). The second group consists of contributions focused on the effects of the expansion on agricultural communities and their territorialities ( ^{Cáceres, Silvetti, Ferrer, Soto, & Bisio, 2009} ; ^{Domínguez, 2010} ; ^{Comerci, 2014} ).

Different studies have addressed the agrarian frontier as their specific object of study and the focus of their theoretical reflections. Their basis is geographical, although they maintain constant interchange with other disciplines; these studies focus on the study of agroindustrial expansion in different parts of the country. Their starting point is the recognition of the specific characteristics of the frontier as a space, and their dimensions of analysis include social conflict ( ^{de Estrada, 2010} ), the relationship between the urban and rural contexts ( ^{Braticevic, 2011} ), and the organization of production systems ( ^{Valenzuela, 2014} ). They consider the agrarian frontier as a process, which is reflected by some of the cross-sectional elements in these studies; they recognize the integrative nature of the space, where opposing projects and logics coexist and resistance and conflict are characteristic.

An interdisciplinary approach profoundly influenced by ecology lies somewhere between these initiatives and those mentioned above. This proposal was developed by the Landscape and Environmental Ecology Group (GEPAMA) from the University of Buenos Aires. Its main interests are changes in land use involving extended areas (transformation of natural or semi-natural ecosystems into agricultural land), and they consider the agrarian frontier as a space that becomes complex and problematic when it is incorporated into the global production system ( ^{Morello, Rodríguez, & Pengue, 2004} ).

INTERNATIONAL BORDERS

The borders that separate national states from one another have acquired a renewed academic interest in various disciplines in Argentina since the late 1990s, for example in anthropology, history, geography, and international relations. These are heterogeneous studies both in their theoretical-methodological strategies and in their study areas and periods, and they use different terms to describe frontiers: international, political, state, interstate, external, physical, territorial, geopolitical, and political.

Anthropological, historical, and geographical studies have proposed critical approaches that, since the 1990s, have renewed the study of these frontiers in major academic institutions in Latin America and Europe. This shift was due to the new challenges posed by national production to traditional perspectives in which borders were static and evident objects, natural and apolitical realities in line with the central position given to the national territory. On the other hand, these new studies conceive borders as processes involving social and historical realities and as a product of dispute and negotiation.

From anthropology, ^{Grimson (2000a)} questions the concept of borders as natural realities or as a result of existing cultural objectivity, but the author also challenges the notion of the brotherhood of peoples permeating integrationist discourse that overlooks the dimensions of conflicts.

In the case of geography, studies by ^{Barros and Zusman (2000)} and ^{Hevilla and Zusman (2008)} propose transcending the classic views in which borders are considered transitional areas separating pure forms; instead, these studies regard borders as places having their own dynamics, agreements, and disagreements. Borders are analyzed in connection with the expansion processes of political and economic organization.

They also point out the need to incorporate cultural processes associated with representations, narratives, and signs into the economic and political analysis of borders, and they highlight the importance of adding heterogeneity to the discussion by incorporating certain borders that the literature has almost ignored.

For their part, ^{Benedetti (2014} , ²⁰¹⁵ , ^2017b) and ^{Benedetti and Salizzi (2011)} have contributed to the conceptualization and operationalization of Argentinian borders. These studies examine the interrelationships between the concepts of territory, boundary, and border, introduce new concepts such as the frontier space, and propose operational categories for their study, such as territorial differentiation, border, territory, place, and mobility.

Some of these studies call methodological nationalism into question. In that view, international borders are assumed to play the role of “hurdles” that promote the autonomous development of individual republics. This group of studies has shown that these borders coexist with social and economic spaces whose scope goes beyond the proximity of international boundaries resulting from the consolidation of modern national states and that the processes leading to their disassembly were delayed ( ^{Bandieri, 2001} ; ^{Hevilla, 2001} ; ^{Conti, 2011} ).

In parallel, other contributions debate the discourse about the end of borders. Thus, although the increased flexibility of the borders is acknowledged as part of globalization, these studies underscore their increased regulation and social control exerted over local populations, even in the context of regional integration initiatives and projects ( ^{Grimson, 2000b} ; ^{Sassone, 2005} ; ^{Hevilla & Zusman, 2007} ; ^{Trinchero & Leguizamón, 2008} ).

In addition to the theoretical contributions of these studies on international borders, many of them represent empirical approaches associated with specific geographical spaces. Some of the most frequently studied areas are the northwest borders ( ^{Karasik, 2000} ; ^{Conti, 2011} ; ^{Benedetti & Salizzi, 2011} ), the Cuyo ( ^{Hevilla, 2001} ; ^{Escolar, 2013} ), the Patagonia ( ^{Bandieri, 2001} ; ^{Baeza, 2008} ), and the Gran Chaco ( ^{Grimson, 2000b} ; ^{Gordillo, 2000} ; ^{Trinchero, 2012} ). Few studies have undertaken to study the country’s borders comprehensively; some of these are the works by ^{Sassone (2005)} and ^{Benedetti and Salizzi (2014)} . Finally, many of the studies focus their attention exclusively on the Argentinian side, failing to account for what happens on the other side of the international border.

We could differentiate two main groups of studies on the basis of the historical periods covered by the literature. One of them focuses on the formation of national states, the borderline demarcation, and the consolidation of border controls throughout the nineteenth and twentieth century ( ^{Gordillo, 2000} ; ^{Karasik, 2000} ; ^{Hevilla, 2001} ; ^{Lacoste, 2003} ; ^{Conti, 2011} ; ^{Escolar, 2013} ; ^{Zusman, 2017} ). In general, they focus on the ways in which national states have created separation, difference, and otherness with respect to their neighboring countries and the local responses to these processes. The other group focuses on the contemporary period and analyzes the implications of regional integration processes (e.g., Mercosur) from different angles and using different scales ( ^{Grimson, 2000b} ; ^{Trinchero & Leguizamón, 2008} ). They describe the effect of states and supranational organizations on the everyday life of the citizens, who are usually excluded from the definition of such organizations.

In general, the traditional view on interstate borders is called into question by these studies. They refuse to see the border as an evident and static object, as a natural reality independent from politics, and reject the essential role given to the territory and international boundaries ( ^{Barros & Zusman, 2000} ); instead, borders are thought as social and historical realities occurring as processes ( ^{Benedetti & Salizzi, 2014} ).

Additionally, these studies bring into the conversation the notion of “top-down” and “bottom-up” frontier construction processes, including the actions carried out by national states and the agency of the multiple types of individuals that live in these frontiers or traverse borders frequently. These studies explore beyond the perspective centered on the national as the only scale of analysis and acknowledge the convergence of different practices, individuals, institutions, and scales ( ^{Zusman, 2006} ; ^{Benedetti, 2007} ).

At the same time, they present the border as a distinct reality, unlike the opposing view, in which borders are typologically the same in all places and all the time. Their proposal is centered on diversity and heterogeneity, and they consider that the mixture of local strategies and those emanating from the national state define the specific nature of each frontier. In addition, these studies evince the increasing importance of combining material and symbolic dimensions, practices, and representations.

The main proposal of anthropological and sociological studies is related to the notion of border as a space of differentiation or separation. On the other hand, economic studies often emphasize a sense of relationship, discussion, and interaction across boundaries. Geographical and geohistorical studies tend to prioritize the permanent tensions between agreement and disagreement, openness and closure, belonging and exclusion, continuity and discontinuity.

On the other hand, the field of international relations—a subdiscipline of political science—has remained somewhat distant from the debate about the country’s interstate borders. Its contributions can be organized around two main themes: a) defense, which consists in studies focused on national sovereignty and foreign policy, and b) studies focused on trade and development in the context of the cross-border cooperation and the commercial mobility agenda imposed by the creation of Mercosur.

In methodological terms, these studies use comparative designs to contrast either countries or blocks (for example, Mercosur-European Union), and they generally disregard case studies due to the concern of the discipline with world orders. Thus, borders are only the outer layer of the nation, which indicates a lack of permeability to the renovation processes undergone by other disciplines. The present study differentiated three stages in the research carried out by this discipline: a) from the end of the nineteenth century to the 1970s, in the context of geopolitics and relationships between neighboring states; b) from the 1950s to the 2000s, concerning the debate between sovereignty and autonomous development, and c) from the 1980s to the present, concerning regional integration processes.

The dialogue between international relations and other social disciplines has been scarce. The main trend, in general terms, is realism, which has a vernacular interpretation known as ‘peripheral realism’ ( ^{Escudé & Cisneros, 1998} ). The work of these authors is based on the idea of sovereignty and development, and the concept of frontier is reduced to a boundary between jurisdictions.

^{Russell and Hirst (1987)} analyze the role of the armed forces in the continent from a defense– and security-centered perspective. In this context, the attention shifts from the interstate border to the struggle against the common enemy. Military logics imply the idea of the border as a containing wall, necessary for national sovereignty. Other authors, such as ^{Russell and Tokatlian (2009)} , focus their work on relational autonomy and reflect on the relationship with neighboring states. The issue of frontiers is not explicitly mentioned, although it is hinted in several arguments.

A study by ^{Tokatlian (2005)} connects the thematic spheres of defense and autonomous development in the context of the global insertion of Argentina. Its theoretical development on sovereignty fails to mention the interstate border, although the paper does include recommendations around the issue of the Triple Border.

The institutionalization of regional integration processes since the 1990s has broadened the scope of international studies and has opened the door to issues such as infrastructure, cross-border mobility, regional external trade, and security. Of particular note in the 2000s are studies analyzing interstate borders based on trade and cooperation perspectives focused on the eventual benefits of openness. Since then, liberal visions have given way to neo- developmental perspectives whose integrationist stance conceives the border as the center of Latin American unity, although it is still analyzed from the perspective of security.

Few studies carry out detailed analyses of specific interstate borders: they are usually analyzed in relation to production zones ( ^{Botto & Tussie, 2007} ; ^{Botto, 2013} ). In parallel, other studies focus on cross-border cooperation, although they also favor a comparative assessment at the national scale ( ^{Rhi-Sausi & Oddone, 1991} ; ²⁰¹¹ ; ^{Oddone, 2012} ). ^{Paikin (2010)} is one of the few authors to propose a concept of interstate border; cooperation is addressed from an institutional perspective, although the author makes a strong emphasis on paradiplomacy and the notion of “border-interest.”

Finally, studies by ^{Bartolomé and Llenderrozas (2002)} on international security and ^{Zimerman (2009)} on Mercosur provide an empirical approach that links political aspects with local analyses. These examples suggest a lack of interest in the formal conceptualization of the frontier: they address the border as a boundary between states. In a similar vein, ^{Malamud’s (2011)} work on microregionalism regards the frontier as a divide between local communities. From this point of view, after analyzing the Mercosur in the light of experiences from the European Union and the Schengen area, the author suggests the need to facilitate cross-border movements by reducing controls and bureaucracy ( ^{Malamud & Schmitter, 2006} ).

URBAN AND PERI-URBAN BORDERS

The study of urban and peri-urban frontiers can be organized based on two main approaches: One of them focuses on the distinction between the urban and the rural contexts and the transitional nature of these spaces. The other approach, perhaps more limited, analyzes the internal ruptures of urban structures and their nature (political, economic, or religious, among others), and its chief reference has been the urban wall.

Concerning the first approach, the notion of peri-urban spaces began to be used in the 1940s by scholars from Anglo-Saxon countries; it was related to urban expansion and the uncertainty of the space between the countryside and the city ( ^{Novick, 2017} ). In the Latin American context, the study of hybridization between the urban and the rural worlds has been relevant since the mid-twentieth century ( ^{Castro, 2018} ). Following this trend, a number of Argentinian authors put forward the existence of urbanity/rurality gradients as a function of the intensity of different elements and processes ( ^{Bozzano & Cuenca, 1995} ; ^{Gorenstein, Napal & Olea, 2007} ); while others have focused on one area of these gradients ( ^{Barros, 1999} ; 2005; ^{Barsky, 2005} ). The terms used to account for these environments are: ‘frontier territories’ ( ^{Bozzano & Cuenca, 1995} ), ‘rururban’ environments ( ^{Barros, 1999} ), ‘peri-urban’ environments ( ^{Barsky, 2005} ), and ‘peri-urban areas’ ( ^{Frediani, 2010} ).

^{Bozzano and Cuenca (1995)} describe three types of land use in the city, which they present as a gradient; these types are subdivided according to their hierarchy: central, intermediate, and frontier. Central territories are characterized by the concentration of economic and social activities. Intermediate territories, associated with social reproduction, are identified as urban tissues characterized by the presence of different types of housing and their irregular consolidation. However, the concentration of activity and population in the frontiers is less evident. Additionally, their specific locations and distributions are not specified. Therefore, central territories can be almost peripheral to the metropolitan spatial configuration, and frontiers can become central. Hence the notions of central borders and peripheral centrality.

^{Barros (2005)} defines rururbanity partaking from both of its ends: the urban and the rural contexts. The author associates the idea of the rururban space with the idea of a rural- urban continuum. This space is composed of gradients, called semi-urban when a rural habitat is combined with urban or industrial infrastructure; and urbanized semirural when urban areas and agricultural activities share space. In addition, the concept of neorurality is associated with the repopulation of rural areas by inhabitants from urban origins (e.g., country clubs or chacras), sometimes associated with rural tourism ( ^{Barros, 1999} ).

For their part, ^{Barsky (2005)} refers to the notion of the peri-urban, understood as a territorial complex expressing an interface between two apparently well-differentiated spaces: the countryside and the city. It is a slippery and fragile concept, difficult to define and delimit, unstable in its social relationships, heterogeneous in its uses, and constantly changing.

Finally, ^{Frediani (2010)} points out that, in a post-industrial context, deconcentrated urbanization creates movement from the center to the periphery (as opposed to traditional flows from the country to the city) associated with the technological advances that allow for communication in rural environments and urbanization initiatives. This author focuses on peri-urbanization processes and the advancement of the components of the urban structure in the rural context. These processes result in the formation of a transitional entity characterized by its dynamism, marked contrasts, and rapid mutations. In general terms, it considers peripheries as socially and culturally heterogeneous, complex, and diverse spaces.

In sum, the urban and rural realms have often been viewed as antithetical. Perspectives based on the former or the later have alternately praised either the urban or the rural. Thus, the way in which such spaces are considered varies depending on the attitudes of the researchers and the construction of their objects of study. However, the studies mentioned above underscore the diffuse nature of this space, characterized by its imprecise location and wide range of uses, where the urban and rural spheres can be reinvented or reevaluated—in any case, the space is neither one nor the other.

The second approach to peri-urban frontiers focuses on cities; it partakes from their recognition as increasingly unequal social scenarios. In this context, new categories are built in order to re-approach social, spatial, and morphological separation processes (and their associated logics), taking place in contemporary urban centers. The following paragraphs describe some of the research carried out in the field of urban studies to establish a conceptual framework for urban frontiers from disciplines such as geography and sociology.

Pioneering work by ^{Torres (2006)} , focused on Greater Buenos Aires, analyzed the physical definition and formation of the structures and centralities of Latin American metropolises. His main argument is that the internal spatial structuring of Buenos Aires is closely associated with the major periods of economic, social, and political change in Argentina. Although this study fails to address the concept of frontier directly, it shows an interest in mapping boundaries separating human groups whose socioeconomic realities are different.

Another referent in this category is ^{Vapñarsky (1984} , ¹⁹⁹⁵⁾ ; unlike Torres, this author is concerned with issues such as the censual definition of localities, and he reviewed the political-administrative partition in different Argentinian cities. Again, the author avoids an open discussion of the category of frontier, but he provides sound methodological tools to address spatial differentiation and fragmentation processes.

Nowadays, the concept of frontier is frequent in urban studies to refer to the material structures that run through the city or the intangible boundaries produced by the social representations of certain spaces. This is the case of ^{Vidal-Koppmann (2005)} , who examined this category in relation to spatial mobility. Thus, the concepts of fragmentation and segregation are connected with the concept of frontier since mobility is necessary to cross any boundary. The author argues that the presence of physical barriers demarcating boundaries is inevitable ( ^{Vidal-Koppmann, 2007} ), although the study lacks a clear analytic differentiation between the concepts.

Finally, ^{Segura (2006)} is probably the author who has contributed the most to the analysis of urban spaces considering the concept of frontier over the past years; he argues that all frontiers are simultaneously separation and union and underscores the importance of analyzing the way in which these two mechanisms are hierarchically organized.

In short, it is also possible to find the category of frontier in contemporary urban studies. In most cases, it refers to the idea of separation among the different fragments that make up Argentina’s large cities. In general, the concept refers to neighborhood walls or the barriers that can result from the presence of sizable road infrastructure projects. These studies open new theoretical perspectives in addition to new methodological approaches to the analysis of frontiers in the social imaginary of urban dwellers.

Urban and peri-urban frontiers are associated with demographic growth, but also with the social problems that emerged in large cities over the second half of the twentieth century. Although these studies use the frontier as a category of analysis, their conceptual development is scant. Studies focusing on the inner workings of urban environments (usually large cities) present a diffuse, imprecisely located concept of frontier, and the concept is given heterogeneous uses associated with the idea of separation (wall or barrier). Research centered on the peri-urban context tends to be richer in theoretical discussion, although its notion of frontier fails to include the most common terms used to characterize the phenomenon. Therefore, the need for new reflections to broaden our conceptual development around intra-urban and rural-urban frontiers in Argentina becomes evident.

CONCLUSIONS

Since the 1980s, several studies focused on Argentina have revisited and reconstructed the concept of frontier. This growing interest in the topic occurred within the framework of a renewal of social studies. The change was characterized by the adoption of critical positions to establish points of contact among contemporary theories and to its interest in new research issues and areas associated with specific contextual transformations.

As a result of this renovation, the attention of researchers transcended the concept of frontier favored by classical approaches, which was limited by the stress given to the national state by its representative authors. Increasing recognition and discussion of other types of frontiers at different scales (and their possible intersections) has followed. In addition, the movement brought into the discussion fields that had been oblivious to the issue of frontiers, which increased the interest of academic research in establishing interdisciplinary interchange, which had been scarce or ineffectual until the shift.

The ensuing diversification of academic production in Argentina has consolidated four main lines of inquiry associated with different types of frontier: interethnic, production- related, interstate, and urban/peri-urban. Each of these thematic areas was constructed in relative isolation from the rest, which has resulted in areas of specialization that relate disciplines, social issues, and types of frontiers, but are scarcely interconnected with one another. A pioneering study aimed at establishing agreement was carried out by Benedetti and Salizzi (2014), who focused more on the analysis of territorial processes (considering interethnic, interstate, and production-related frontiers) than on the theoretical- methodological aspects of their study.

The growing diversity of approaches and the scarce dialogue among the specialization areas is associated with the recent consolidation of this field of study in the country. This is reflected, for instance, by the scarcity of specialized scientific journals (unlike countries such as Mexico, Colombia, Brazil, and Chile). TEFROS, a journal edited by the South Border Ethnohistory Workshop since 2003, which specializes in interethnic frontiers, is probably the only example of this type of literature.

Despite their compartmentalization, the different lines of inquiry share common questions concerning social phenomena involving some form of discontinuity or spatial fragmentation. The literature reviewed for this paper demonstrates that the concept is gaining visibility and attention and that the framework of perspectives and stances concerning the different types of frontiers is positively heterogeneous in its interests, approaches, and methodological practices. Therefore, subsequent research should increase the focus on reflections integrating the different contributions to the study of frontiers. In addition, individual disciplines must establish connections with other disciplines in order to share both theoretical perspectives and types of frontiers addressed so that their range of resources and contexts of application is maximized.

The present paper sought to reconstruct and systematize the various lines of research that shape this field of study. We now face the challenge of fostering more theoretical- conceptual reflection that will contribute to establishing new connections among the different disciplines, perspectives, and research interests.