This book is the third in a series, following Legitimacy in International Society (2005) and International Legitimacy and World Society (2007), in which Ian Clark has applied the concept of legitimacy to the English School's way of thinking about both international society (the society of states) and world society (global civil society mainly in the form of nonstate actors). For Clark, legitimacy is what defines both rightful conduct and rightful membership in society. Following the English School tradition, his main focus in terms of rightful conduct is on the primary institutions of international society: such deep practices as sovereignty, nationalism, diplomacy, the balance of power, great power management, and the like that constitute both the actors and the rules of the game of international society. This approach contrasts with the focus on secondary institutions—intergovernmental organizations, regimes, and other consciously constructed, instrumental entities—that is characteristic of liberal approaches to International Relations.

Here Clark's aim is to consider whether and how hegemony can be considered as a primary institution of international society; in other words, whether the primacy of a single state can be legitimate. His main concern is not to advocate or criticize hegemony as such. Rather, he is more interested in norms as social structure—as a way of understanding what is, and can be, understood as legitimate in the society of states. What is legitimate is not always nice: in the past both colonialism and human inequality (slavery, racism) have been primary institutions of international society. As in the two earlier books, Clark's approach is to offer a theoretical framework and then to apply it to a series of historical case studies. In this instance he looks at the Concert of Europe and Britain during the nineteenth century, the Pax Americana from 1945 to 1971 (when the United States abandoned the Bretton Woods arrangement), and three more recent case studies of hegemony in action—namely, reform of the UN Security Council, regional relations in East Asia, and the negotiations over climate change.

Clark's principal target is the materialist logic that dominates all forms of realist and much neoliberal thinking about hegemony. He is therefore at pains to distinguish between primacy (or unipolarity), which covers a material distribution of power skewed toward a single state, and hegemony, which is a social condition in which the right of any actor to lead is acknowledged by a substantial group of followers. Hegemony is not, as the materialists would have it, simply an epiphenomenon of a lopsided distribution of power, but rather a social position given to a leader by its followers. In Clark's scheme, primacy without hegemony is perfectly possible. In principle, hegemony without primacy might also be possible, following the logic of religious leaders, such as the Pope, though Clark does not delve into this in any depth. This is where the English School comes in. One of the primary institutions in its classical literature is great power management. In English School thinking, great power status is itself a social construct, in which leading states both claim and are given managerial responsibilities in relation to international order. It is from this idea that Clark convincingly builds an argument that hegemony might also be legitimate in this sense.

However, his choice of the English School as the context in which to pursue this argument is a brave one because much of its classical literature is hostile to hegemony. So Clark has not only to take on the materialists, but he must also take on his allies in the English School itself. Here the Zeitgeist is with him. The classical English School rooted its concept of international society in an anarchic structure, and mostly wedded itself to the idea that it was only within a balance of power that international society could emerge. If one state disabled the balance by achieving primacy, it would be able to lay down the law to the others, so replacing international society with empire. Hegemony was thus the antithesis of international society. This way of thinking is close to Kenneth Waltz's idea that anarchy requires at least two great powers. But even within the classical English School there were voices arguing for the need to push the idea of international society, with its rule of consent, beyond anarchy to hegemony; and more recently there has been a flow of literature concerned with the contradiction between the principle of sovereign equality underlying international society and the practice of degrees of hierarchy, not just reflecting the demands of American exceptionalism and primacy but also in such secondary institutions as the UN Security Council and the International Monetary Fund.

Clark thinks that the English School needs to be saved from itself on this point, so that it is more able to use its international society approach to think about the current partly hierarchical realities of world politics. He is correct in this, and his book represents a major advance in this literature. His analytical scheme, and his application of it to cases, shows real elegance. He distinguishes between singular (one superpower) and collective (a concert of great powers) hegemonies, and between hegemonies that apply to the whole of the international system and those that apply to some coalitional subsystem. This latter distinction works particularly well to enable him to unpick the U.S. case and to expose the oversimplification of the materialist approach. He sees the United States as mainly a singular hegemon within a coalition. Its claim to global hegemony is much weaker, and it is repeatedly torn between maintaining its singular hegemony and moving toward a collective one. Using his lens of legitimacy, Clark exposes interesting dynamics of the tensions between legitimacy and efficiency in the leadership of international society, and of the legitimacy pressures on singular hegemons.

This is a fine and thought-provoking book. In my view, Clark successfully makes the case for hegemony as a possible primary institution of international society, and this is a signal service to the English School. He also neatly exposes the limitations of materialist approaches to hegemony. The main problem of the book is that the application of the scheme to the cases gets increasingly complicated. By seeing his two pairs of distinctions as spectrums, Clark rightly opens up the detailed dynamics of hegemonic politics in his cases, but at the cost of creating a rather fluid and multilayered image of hegemony that is considerably harder to grasp than the simplicities of the materialist alternative. And by breaking up the last three case studies into issues and areas, the book somewhat loses focus on the U.S. case after 1971. There are many interesting insights into aspects of current U.S. hegemony, but no really clear overview. Given the return to fashion of U.S. declinism, readers might have welcomed more of an attempt to apply the scheme to look forward not just in specific issue areas but in the process of hegemonic transition as a whole. But these are quibbles to the main event. By bringing legitimacy to bear, Ian Clark has opened up a new and debate-changing way of looking at hegemony. Hats off to him.