The United States is today a global superpower without historical precedent. It stands at the centre of an expanding democratic-capitalist world order that is itself, fifty years after its creation, the dominant reality in world politics. Despite expectations that American hegemony would disappear and trigger the emergence of a new and unstable multipolar post-Cold War order, the opposite has in fact happened. American power has grown even greater in the decade since the collapse of the Soviet Union. Although American power is not uniformly welcome around the world, serious ideological challengers or geopolitical balancers are not to be found. Scholars who a decade ago were debating the prospect of co-operation and conflict in a post-hegemonic world are now debating the character and future of world politics within an American unipolar order.

In a recent article in the Review of International Studies, Stephen Hobden does a great service by initiating a critical evaluation of the potential for historical sociology in international relations theory. Hobden considers seminal studies by Michael Mann, Theda Skocpol, Charles Tilly, and Immanuel Wallerstein, and concludes that each is inadequate for building an historical sociology of the international system. Articles such as Hobden's are particularly important in international relations, where many major theories are dependent upon the assumptions and methods of other disciplines. From time to time, we need to ask, in a comparative manner, just how useful such methods and assumptions really are.

Fred Halliday, Revolution and World Politics: The Rise and Fall of the Sixth Great Power (London: Macmillan 1999).

In an age which seems anything but revolutionary it is essential to recall how much the international politics of the last two centuries has been shaped by the fear - real and imagined - of the revolutionary overthrow of the existing order. It all began of course in France, continued with the Bolshevik seizure of power in 1917, and then persisted in one form or another for the entire duration of the two post-war periods.

Rudolf Kjellén was an important political scientist during the first half of this century. He is perhaps the most influential Scandinavian political scientist ever. Together with the political geographer Fredrich Ratzel, Kjellén was the founder of the German geopolitical school. All his major works were translated into German, but they were, to my knowledge, never translated into English. They were important sources of inspiration for the leading geopolitical theorist and military general, Karl Haushofer.Karl Haushofer, Grenzen in ihrer geographischen und politischen Bedeutung (Berlin Grünewald: Kurt Vowinckel Verlag, 1927); Dan Diner, ‘Grundbuch des Planeten’—Zur Geopolitik Karl Haushofer, Vierteljahrshefte für Zeitgeschichte,32: 1 (1984), pp. 1–28; Barbro Lewin, Johan Skytte och de skytteanska professorerna[Johan Skytte and the Skyttean Professors]. Acta Universitatis Upsaliensis (Skrifter utgivna av Statsvetenskapliga föreningen i Uppsala, 100), (Stockholm: Almqvist & Wiksell International, 1985); Rainer Sprengel, ‘Land und Meer—Eine diskursanalytische Betrachtung’, WeltTrends (1994), pp. 61–84. By the time of his visit to Sweden in 1935, Haushofer was about to publish the 25th German edition of Kjellén's Die Grossmächte [The Great Powers].Edward Thermænius, ‘Geopolitik och politisk geografi’ [Geopolitics and Political Geography], Statsvetenskaplig tidskrift, 19 (1937), pp. 213–328. The idea that states were not fixed juridicial entities but dynamic organisms competing on the international scene, was something that appealed to Haushofer. He was to fuse this thought with Ratzel's concept of Lebensraum, that was later to reach Hitler.

I would like to thank Daniel Nexon for taking the time to read, reflect, and comment on the article ‘Theorising the International System: Perspectives from Historical Sociology’. His comments are astute, pertinent and challenging. I would also like to thank the editors of the Review of International Studies for offering me space to reply to Nexon's comments. Nexon clearly wishes that I had written a different article. However, although I think that the article he has in mind is one that should be written, I had different intentions in mind. Nexon is clearly doing a big service to International Relations scholars by introducing them to relational sociology, but this was not what I set out to do. I will start therefore with some comments on my intentions in writing the article. I will then offer some points of clarification. Finally I will address Nexon's major criticisms of the article: my failure to acknowledge relational sociology and my critique of the analysis of international systems in the works of Tilly and Mann. My overall argument will be that the dichotomy that Nexon offers between neofunctionalism and relational sociology is not as straightforward as he suggests. He acknowledges this in his final footnote, and it is a point also conceded by Emirbayer in the article that Nexon primarily draws upon. Furthermore, on this point, I think that we share more common ground than Nexon would wish to acknowledge. However our positions on structures are radically different. On this point our differences are, I believe, irreconcilable. What I will attempt to argue is that there are fundamental differences between material and ideational structures which makes it difficult to analyse them cumulatively.

Russia is by some measures the most successful imperial enterprise in history. Surpassed in size only by the British and Mongol empires, Russia and its Soviet successor proved far more durable than either one. It retained its peak territorial extent longer than any other empire, and for most of the last 400 years it has been the largest polity on earth. Moreover, both St. Petersburg and Moscow were hugely successful as great powers, playing major roles in European and world politics for the three centuries after 1700. And their influence as great powers peaked in the nineteenth and twentieth centuries—an era in which states based on nations appeared to have the competitive edge over old-fashioned polyglot empires.

The fascination of revolutions is one shared by the worlds of scholarship and art and literature alike. For the latter, revolutions appear to hold out hope that a new order will sweep aside the decay, oppression and corruption they perceive as omnipresent in society. For the former, revolutions come tantalizingly close to the holy grail sought by social scientists for two hundred years, offering sequences of events and patterns of interaction that share sufficient similarities across continents and centuries to suggest the possibility of a true science of human affairs, including predictive hypotheses.

Over the course of its twenty-five year history, the Review of International Studies has been an important outlet for articles that sought to define an English School.As have other European-based journals, particularly Millennium, Cooperation and Conflict, and more recently the European Journal of International Relations. At the time of the first volume of the British Journal of International Relations—as it was then called—in 1975, there was a growing sense of a divided discipline. Alienation from the agenda being put forward in the US was compounded by greater introspection about what, if anything, unified the International Relations community in Britain. Early attempts to advance a different agenda were published in the BJIR by (among others) writers such as Hedley Bull, Alan James and R.J. Vincent.

This collection of essays grapples, historically, with the complex issues involved in understanding system transformation. Often these transformations have taken the form of a shift along the spectrum of independence-centralization, and it is within the framework of such declining or emerging imperial systems that the degree of change has tended to be measured. The task of this contribution is to locate the specific case of the end of the Cold War within the broader reflections on these themes. It will respond to this challenge by applying a different litmus test for change from that already found in the existing literature about the significance of the end of the Cold War. Instead, it will broach the topic by an examination of prevailing concepts of legitimacy within international society. In short, it argues that a study of the role of legitimacy might be a useful way of documenting and measuring the kinds of changes taking place within an international system. Moreover, while the end of the Cold War might be thought to have nothing to say about the issue of empire as such (beyond recording the expiry of the Soviet version), it will additionally be suggested that the resultant extension of shared concepts of international legitimacy can be understood as a defining attribute of the contemporary imperial project.

Fred Halliday has been impertinent enough to write this book at a time when the collapse of the European socialist bloc and the undiluted hegemony of a trans-nationalized capitalism, encourages the beatific neo-liberal confidence in the ‘end of history’. For this book brilliantly emphasizes the meaning and the importance of revolutions both as an historical phenomenon and in terms of its relevance for the twenty-first century, especially for those countries of the South. Probably few academics in Western countries are as well positioned as Halliday to write about the subject: his early links with the New Left in the 1960s, his interest in the study of Third World conflicts and revolutions, and of course his role as a theoretician of international relations, have equipped him well. His study analyses revolutions in all of their complexity and range, from the British to the Iranian, the French to the Bolshevik, the Chinese to the Cuban. The result is a substantial, profound, richly analytical book, that almost requires writing another book to discuss its various qualities. I will however restrict myself here to making a few comments about the issues I deem particularly significant.

A sea change of major proportions is taking place in the historical social system forming the modern world, creating a widespread sense of uncertainty about the present and foreseeable future. In the words of Eric Hobsbawm, as ‘the citizens of the fin de siècle tapped their way through the global fog that surrounded them, into the third millennium, all they knew for certain was that an era of history had ended. They knew very little else’.

This is a rich, impressive and timely book. At a time when American and neoliberal triumphalism deny the significance of any revolution later than 1776, and when almost no-one in the social sciences is still studying either revolution or class, Fred Halliday has demonstrated that we have been living in a revolutionary age, dominated by the conjoined effects of war and class revolution. In case you find his sub-title mysterious, Karl Marx noted that the Europe of his time was dominated by five Great Powers, but Revolution, ‘the sixth Great Power’, would soon overcome them all. Halliday would suggest that Marx was only half-right. Revolution did not overcome all five Powers, but it did transform them all—and their successors. Hannah Arendt and Martin Wight also emphasized that couplings of war and revolution have dominated much of modernity. But Halliday adds that these are not to be seen as ‘disruptions’ of International Relations, they are International Relations, since they have set the overall parameters of the modern international system. They did so, he says, in three distinct revolutionary phases from the sixteenth century to the present-day: sixteenth-seventeenth century religious wars/revolutions, late eighteenth and early nineteenth century Atlanticist wars/revolutions, and twentieth century wars/revolutions which became increasingly dominated by communism.

I was greatly encouraged by the present proposal to relaunch the concentrated dialogue of the British Committee for the Theory of International Politics, and by the positive response of the many leading scholars listed in Barry Buzan's article ‘The English School: an Underexploited Resource in IR’.

The working methods of the original Committee are well summarized in Buzan's article, and those methods and the scope of its enquiries are described more fully in Tim Dunne's most useful history of the English School of IR, Inventing International Society.Tim Dunne, Inventing International Society: A History of the English School (London: Macmillan, 1998). There is thus no need to look back over them here.

Over the past quarter-century, Fred Halliday has distinguished himself as a prolific and insightful scholar of international affairs. He has imbibed a generous dose of Marxist theory without being intoxicated by it, and one might say the same for his consumption of other types of theory as well. Not content to be an armchair academic, Halliday is personally acquainted with a number of revolutionary movements and his writings combine an obvious sympathy for their aspirations with a clear-eyed sense of their shortcomings. The result is a combination of intellectual range and personal experience that is nearly unique among contemporary scholars of world politics.

Policymakers and scholars have to deal with the difficult problems of variation, change, and transitions in world politics. Practitioners have to estimate the capabilities and intentions of those with whom they are interacting and need to determine the kind and extent of variety in their environments. Detecting, diagnosing, and dealing with change also is particular difficult. Scholars have shown the wide range of units and systems that human beings have created, but need to also examine the extent to which they are characterized by common processes and dynamics. The balance of power generally operates through unintended consequences and can characterize systems even when no one seeks balance. Change may be more common than scholars often appreciate. Nuclear weapons undermine much traditional international politics and even greater changes will flow from the fact that the leading powers in the world no longer contemplate war with each other.

The English School is an underutilized research resource and deserves a larger role in IR than it currently has. Its distinctive elements are its methodological pluralism, its historicism, and its interlinking of three key concepts: international system, international society and world society. International society is the main focus, and the via media, between the other two, but more work needs to be done to develop the School's theoretical position, particularly in understanding the relationship between international and world society. In order to realize its potential, the English School needs both to construct a more coherent research agenda and to recover some of the working method of the British Committee. It is potentially a way of challenging the theoretical fragmentation that afflicts IR, and of setting up the foundations for a return to grand theory.

I support Buzan's call for a reconsideration of the English School as an important approach to International Relations. The challenge is to avoid introspection and scholasticism (is it a school? who belongs? what are the core articles of faith?) and instead to use the intellectual apparatus provided by English School ideas to raise interesting questions, identify intellectually important puzzles, and to help structure answers to real moral and political dilemmas. In this comment I would like to raise five issues.

No author of a study such as mine could fail to be grateful, to editors and contributors alike, for a discussion as wide-ranging and pertinent as that which the Review has accorded my book on revolutions. The main purpose of Revolution and World Politics was to place the study of revolutions, as historical process and as theoretical challenge, at the centre of International Relations. The responses printed here seem, in large measure, to reinforce that endeavour.

The Forum should not be too cosy, said the editors. But in many regards, Barry Buzan's invitation to put to better use the resources of the English School makes criticism difficult. Who is going to oppose, in principle, a more concentrated effort in international theorizing, methodological pluralism, substantial openness to sister fields and disciplines, linked to a general endeavour for giving some coherence to the diverging theoretical interests? Moreover, who can criticize the very fact that somebody wants to pool existing resources for pursuing research, before seeing the outcome?

Hence, the following remarks can hardly be against the open project as such, which I wish much success. It will be directed against some particular ways to fill it out, ways which are often, I think, not intended by Buzan himself. In other words, the discussion is as much about analysing Buzan's paper as about pre-empting particular ways to read it. To caricature the position: if the project becomes understood as too English and US-targeted, too encompassing and too traditional, the English School might well remain an underexploited resource.