The fashion for writing books on international affairs with the word ‘empire’ in the title may now be coming to an end – just as historians are starting to join it. The trend began in the United States before the drama of 9/11 but expanded greatly thereafter, and five years later has produced libraries of books and essays that brandish the term and draw on its history. Non-historians whose interests lie in the present, and whose main aim has been to justify or condemn the appearance of a putative American empire in the Middle East, have written virtually all these publications. Now that the likelihood of establishing a new Western empire in the region is minimal, the rhetoric that accompanied strident recommendations for establishing a ‘benign’ form of imperialism to run the world has largely evaporated, and the most blistering denunciations of the attempt have ceased to be immediately relevant. Accordingly, the demand for partisan studies of what looks like being a failed experiment is likely to subside, though the post-mortem will doubtless be prolonged and commentary about the Middle East will, of necessity, continue.

Although the word ‘empire’ frequently appears in the titles of recent books and articles dealing with America’s global power, the expectation that this will lead to an exploration of the complexity of the term is rarely met. The history cited is often treated as a set of stepping stones to the present or mobilized selectively to verify the political viewpoint of the author. Nevertheless, the new literature has turned over some of the fundamental analytical questions in imperial history for fresh inspection and in doing so has offered an implied challenge to historians to review their own key assumptions. Two of the most important and contentious of these questions turn on the related problems of definition and comparison.

The problem of definition has been the subject of some trenchant exchanges between those who contend that the United States is an empire and those who hold that it is not.Footnote ¹ The claim that the United States is an empire requires its advocates to adopt a definition that encompasses the overwhelmingly informal nature of American power. Taking this step makes it possible to relate the current predicament and actions of the United States in the Middle East to the history of previous empires. The line of descent goes back as far as Greece and Rome,Footnote ² though it rarely extends beyond the Western world.Footnote ³ Conversely, those who deny that the United States is an empire confine the term to its formal components. This definition implies that the position of the United States at the beginning of the twenty-first century is unprecedented. If this is the case, a wholly new appraisal is required to underscore the unique character of world’s first real superpower.

Resolving the definitional question evidently has implications for the way history is used and particularly for the selection and interpretation of comparators. If the United States is held to be an empire, the life cycle of previous empires can be plotted either to reveal ways of avoiding the mistakes that brought down empires in the past or to demonstrate that decline is inevitable, and perhaps even imminent. Commentators who favour empires, or at least believe them to be indispensable agents of global stability, can interpret history to validate an expanded world role for the United States while also promoting an improved model, a ‘benign’ or ‘co-operative’ empire designed to fit the conditions of the twenty-first century.Footnote ⁴ Those who believe that empires have been agents of subordination and oppression harness their view of history to recommendations designed to prevent a new rogue elephant from trampling on the international order.Footnote ⁵

The main difficulty attached to the claim that the United States is an empire, whether benign or malign, is that it stretches the concept across a large number of very diverse circumstances. A record that extends from Greece and Rome to the present is impressive but requires a definition of empire that is so general as to cause doubt about whether like is being compared to like. The contrary assertion that the geo-political status of the United States is without historical precedent builds on assumptions about its ‘exceptional’ character and the distinctiveness of its overwhelming power. This starting point is usually history-free, or at least history-‘lite’, and allows the United States to make a providential appearance – in one interpretation in the guise of a gentle giant, a Goliath who can impose order on an inherently anarchic world.Footnote ⁶ The task of identifying appropriate historical comparisons, though avoided, is not solved. History is still required, even if it is not called on, because, as Marc Bloch pointed out long ago, comparisons are needed to establish singularity as well as similarity.Footnote ⁷

From Romulus to Rumsfeld

The debate about the American empire is consequently one that is inseparable from the historical record and, by inference, requires the participation of historians themselves. So far, however, the views of historians of empire have not been prominent in the public domain, at least in the United States, in the years since 9/11 either because they have been reluctant to become professionally involved in the analysis of current events, or because they have had difficulty in getting their voices heard.Footnote ⁸

The publication of books by two distinguished practitioners, Charles Maier and Bernard Porter, whose thinking has been influenced by the invasion of Iraq, is therefore to be welcomed, especially since they address problems of definition and produce comparisons that draw on extensive knowledge of the past. Maier turns his attention to empire having previously specialized in the history of continental Europe in the twentieth century. His substantial book contains a wealth of references and is directed primarily at a scholarly audience. Porter, a noted specialist on the British Empire, adds an American dimension to his previous work. His book is short, deliberately limits the number of citations, and is written explicitly as a polemic that aims to make a ‘contribution to the current political debate’ (p. 11).

Maier’s book is divided into two approximately equal parts. The first part, entitled ‘Recurring structures’, deals with problems of definition, types of empire, motives for empire-building, imperial frontiers, techniques of management, and the consequences of losing control. The discussion presents an impressive amount of information and ranges widely across the centuries and the world. Tacitus rubs shoulders with Zbiginiew Brezinski; the Austrian and Indonesian armies jostle each other in suppressing resistance movements in different continents and centuries. The second part of the book, ‘America’s turn’, narrows the focus to the United States and to the period after 1945. Three substantial chapters cover the Cold War, the growing economic power of the United States after the Second World War, and the shift from what Maier calls ‘an empire of production’ to ‘an empire of consumption’. The book concludes with some reflections about whether the United States is likely to pursue a path leading to empire.

A book that ranges as widely as this one faces its own problems of managing insurgent thoughts and suppressing rebellious facts. The situation calls for the firm hand of direct rule backed by military discipline of the kind the author finds in the empires he discusses. Unfortunately, Maier’s erudition and admirable sense of the complexity of both the evidence and the issues have prevented him from skewering his data with an argument that runs through the book. There are many probing questions, but no focused thesis.

Maier begins promisingly by raising the question of definition at the outset (p. 2), but immediately states that he has ‘decided to avoid claiming that the United States is or is not an empire’ (p. 3). Instead, he argues that ‘the United States reveals many, but not all – at least not yet – of the traits that have distinguished empires’ (p. 3). This is a curious as well as a disappointing conclusion because the varying definitions of empire Maier then offers include one that would appear to admit informal as well as formal means of creating ‘subordination in international affairs’, and would therefore seem to allow the United States to qualify (p. 7). Elsewhere, however, he reserves the term for a ‘territorially extensive structure of rule’, which would appear to exclude the United States’ (pp. 31, 109). These well-observed but shifting definitions prevent Maier from developing a clear argument and diminish the interest of his historical evidence. This weakness pervades the book as a whole and is the more regrettable because it could have been corrected. Failure to determine a definition that meets all cases does not preclude the possibility of arriving at one that fits the author’s particular purpose. Readers can then judge whether the definition offered is adequate for the task in hand and, beyond that, whether it serves a wider aim or acts as a limiting case.Footnote ⁹

If we do not know what an empire is, it is hard to see how comparisons can be pursued with any rigour. Maier states that his study is an ‘exercise in comparative history and politics’ (p. 3), a theme that he pursues through an extended exploration of imperial frontiers in chapters 2, 3 and 4. We learn that frontiers were important points of imperial expansion and defence, that there were differences between frontiers of contiguous territory and frontiers of overseas possessions, and that the frontiers created by dynastic states differed from those formed by nation states. But the conclusion that frontiers were ubiquitous and varied is insufficiently specified to allow readers to see what case is being argued. This weakness might have been overcome had the author tied his discussion more firmly to the existing historiography. Many of his citations, especially those relating to Europe, will be instructive for historians of modern empires. However, had he used the notable contributions of Hancock, Galbraith, Darwin, and Newbury, among others,Footnote ¹⁰ his analysis of imperial frontiers would have been more focused.

The link between the first and second parts of the book is provided by the idea that the USA created new frontiers after 1945. The discussion that follows compares these frontiers to the ones created by the British and Soviet empires, but the comparison is insufficiently precise to direct the text, which consists of a detailed narrative of US foreign policy during the Cold War. This is Maier’s home ground and he is clearly at ease on it. The outcome, however, is an excessive concentration on Europe and a neglect of Africa and Asia, where decolonization was taking place and subordinate states were being assembled and pulled into line.

The two final substantive chapters (5 and 6) deal with the domestic basis of US expansion. Chapter 5 provides a clear and helpful treatment of what Maier calls ‘an empire of production’, by which he means the industrial and financial power of the United States after 1945. The imperial aspect of US power, however, remains obscure, not least because the main examples of US influence are drawn from Europe, which is a rather special case. A fresh look at William Appleman Williams’s thesis that manufacturers who needed outlets for their products drove American expansion might have helped to make the connection, but Williams is not mentioned in the citations to this chapter.Footnote ¹¹

Chapter 6 deals with the ‘empire of consumption’ that arose in the last quarter of the twentieth century. The chapter conveys a good deal of valuable information about the development of the American economy, but the imperial dimension of the trends remains obscure. It is undoubtedly the case that, as the United States become increasingly engaged with economies beyond its borders, it has also has come to depend on foreign lenders to fund its external and federal debts. However, it is not clear why these trends should be described as forming an empire rather than as being significant developments in recent international economic history. Indeed, empire, as conventionally understood, is dealt with sparingly. There is little discussion of America’s relationship with the ex-colonial world, or of the associated notion of neo-colonialism and its applicability in the late twentieth century.

Maier’s final chapter opens with a highly compressed summary of imperial influences on the Middle East and concludes with some brief speculations about whether the United States will ‘slide towards empire’ (p. 294). The insularity of these speculations, which are cast as matter of choice for the United States, reflects a general limitation of the literature on the new American empire: the values and viewpoints of those on the other side of the frontier are rarely given the weight they deserve, policy-making would seem to require, and time has now allowed, given that the post-colonial era is half a century old.Footnote ¹²

From Palmerston to Powell

Bernard Porter’s book is entirely different. It offers a definition of empire, albeit a generous one, but it limits the risk of trying to compare too many dissimilar entities by confining the analysis to Britain and the United States. The book also has a clear argument, which is to show that British and American empires have much more in common than the new literature allows: the British were significantly less imperialistic than is often thought; the United States has been, and remains, a good deal more imperialistic than is customarily acknowledged. The argument is joined to a ‘frankly political agenda’ (p. 11), which is critical of empire-building and hostile to its consequences.

Porter’s starting point aligns him with FergusonFootnote ¹³ to the extent that both agree that the United States has been reluctant to accept its imperial legacy and current imperial role. Porter, however, departs from Ferguson by concluding that the expansion of the American empire will follow the course of the British Empire in having repressive and racist consequences (p. 7). His purpose here is to alert readers to the evils that accompany empire, even if its advocates have benign intentions. Accordingly, Porter dissents from Ferguson’s prescription that ‘failed states’ should be subjected to long-term imperial rule. The analysis takes a final turn in suggesting that similarities and continuities between the two empires were broken after 9/11, when the United States became what Porter terms a ‘superempire’ marked by overwhelming military power and seemingly limitless ambition (pp. 95, 112). Today, the United States ‘exceeds any previous empires the world has ever seen’ (p. 162).

The argument that the British Empire was far less powerful than many recent commentators have assumed draws heavily on Porter’s own major study, The absent-minded imperialists, which concluded that public awareness of, and involvement in, the empire was far more limited than has been thought.Footnote ¹⁴ In Porter’s view, lack of popular commitment was a sign of vulnerability because support for empire was neither widespread nor deep, and therefore could be withdrawn easily. Britain had very little control over events on the continent of Europe, and she struggled overseas, too, after the Indian mutiny in 1857. Even though Britain acquired territory in Africa and south-east Asia, expansion brought some spectacular defeats, stimulated widespread resistance, and generated increasing concern about the costs of running an extended imperial system. British power was an ‘illusion’ that ‘almost collapsed’ after the First World War (p. 34). Thereafter, the empire survived by a mixture of luck, bluff and repression. The means were too limited to bring significant economic development, and too authoritarian to lay the foundations of democratic nation states.

The United States, on the other hand, was not only a ‘fundamentally expansionist power right from the beginning’ (p. 65) but was an imperialist one too – if the term is used to refer to informal and not just to formal empire. Porter lists the formal expressions of empire-building, notably those following the war with Spain in 1898. Inevitably, though, it is informal empire that claims his attention, beginning with the westward expansion propelled by America’s sense of manifest destiny, continuing with the imposition of open door policies on Japan and China, and growing extensively after the Second World War, when the United States became ‘far more dominant, and therefore in some sense more “imperial”, than her predecessor ever was’ (p. 88).

The book concludes with brief accounts of how the imperialist tradition in the United States became caught up in the events of 9/11, how the revival of imperial patriotism under Margaret Thatcher was continued by Tony Blair’s Labour Party, which added a strand of liberal interventionism, and how the two came together and were directed into the invasion of Iraq. The rest is not quite history but, as these two books attest, is now becoming so.

Porter’s study is a valuable corrective to the argument popularized in recent years that the United States should establish a ‘benign’ empire to solve the ‘problem’ of failed states and associated terrorist activities.Footnote ¹⁵ The argument was never more than a mixture of hope harnessed to selective experience. The hope was inspired by the ideology of American exceptionalism and stressed the superiority (as well as the universality) of the values developed in the United States. The experience cited was principally that of the British Empire, which was used to demonstrate the benefits brought by empire but not to emphasize, in equal measure, the costs.

Any assessment of Porter’s book has to keep in view the fact that it was designed as a polemical contribution to the current debate about whether the United States is or ought to become an empire. The book has been written, of necessity, in some haste. Readers who know Porter as a master-stylist with a sharp eye for the apt phrase and telling quotation may be taken aback on this occasion by the waterfall of words that flow into huge sentences and lengthy interpolations. The prose succeeds in conveying a sense of informality but it also raises questions about whether the thought is always more precise than its expression. The reader is occasionally halted by large statements that the author has not allowed himself time to reflect on. ‘Whoever heard of a business aiming for stability?’ is a question posed as if a response is unnecessary (p. 67). The answer, surely, is a monopoly. Still, if Orwell’s stylistic recommendations have not always been followed on this occasion,Footnote ¹⁶ points of pedantry, once noted, should be set aside and the argument given full measure.

By confining his argument to a comparison between Britain and the United States, Porter is able to engage with the current debate about empire without having to juggle, as Maier has to, with multiple disparate ‘empires’ across the world and over the centuries. It is sufficient for Porter’s purposes to show that Britain and the United States were expanding capitalist nation-states with a common desire to act imperialistically, that is to exercise power over others (p. 2). Beyond this point, Porter is disinclined to dwell on what he calls the ‘semantics’ of empire (p. 2). In his view, the term ‘imperialism’ can be used ‘in any way you like (so long as you make that usage clear)’ (p. 2). Since Porter’s own definition is a broad one, and includes informal as well as formal expressions of imperialist impulses, the United States meets the test and qualifies as being an empire.

Although this approach is adequate for Porter’s polemical objective, it leaves some important issues unexplored. Both powers may qualify to be called empires if the term is used in a very general sense, but the very general sense may not be the most illuminating basis for making comparisons. The features shared by the two imperial powers may also be common to great states that are not thought of as being empires. What is then being examined is the exercise of state power in international relations rather than the specific forms of power captured by the term ‘empire’, in which case imperial analogies may be unnecessary. Moreover, the broader the definition of the terms involved, the easier it is to identify information that fits the intended comparison. Although Porter is concerned to emphasize similarities, his account also shows that Britain and the United States had different motives and imperial structures, even though both acted imperialistically. The differences may be more instructive than the similarities in understanding the context and behaviour of the two powers. If this is the case, applying the term ‘empire’ to both suggests a greater degree of uniformity than the evidence warrants. Ultimately, semantics do matter. If the United States is an empire, the history of similar empires may enable valid comparisons to be drawn. If it is not an empire, or if it is an empire of a very different type, the imperial analogy will be either inappropriate or of limited value.

Assuming, for purposes of discussion, that the comparison between Britain and the United States as imperial powers is valid, the important historical question concerns the robustness of Porter’s central thesis that Britain was less imperialistic than has often been thought and that the United States is more so. The argument that public interest in and knowledge of imperial affairs in Britain was less than has been claimed has consequences mainly for cultural and social history rather than for imperial policy. The general ignorance of the populace was not directly relevant either to the formulation of imperial policy or to the management of empire, especially since Britain remained a limited democracy in the nineteenth century. The elites who controlled policy were better informed about empire and more committed to it than was the mass of the population. Ignorance of empire may even have allowed parliament to approve acts of imperial expansion; greater knowledge might have curtailed it. Today, the citizens of the United States are notably uninformed about the outside world, but their ignorance has not hindered the rise of what Porter calls a ‘superempire’; on the contrary, fear of the unknown, especially the unknown foreigner, enabled politicians to mobilize popular support for the imperial adventure that followed the events of 9/11.

Porter illustrates his thesis by observing how British rule was circumscribed and resisted, despite the fact that large areas of the world were coloured red on the map. This is undoubtedly true, but to show that the reality fell short of the ideal is not to show that it was insubstantial or to deny that the components of the formal empire were crucial subordinates in key areas of foreign and commercial policy. It is also the case, as Porter suggests, that members of the informed elite expressed anxiety about the solidity of Britain’s status as a great power from the late nineteenth century onwards. But this is to be expected: only great powers have anxieties about becoming weary Titans; fear of falling never strikes those who are at the bottom. The appropriate comparison here is with the United States, which currently disposes of the world’s largest military power yet is in a state of permanent alarm about the supposed grave threats posed by minor states with limited firepower.Footnote ¹⁷ Porter cites the concerns about national decline to argue that Britain was not as powerful, or at least as confident, as has been thought. But similar worries are equally relevant to an understanding of the United States today, which Porter considers to be a superpower without precedent.

Porter’s argument is also weakened by two large and puzzling omissions. The first is the absence of even a summary account of the economic significance of the empire. Economic ties between Britain and her (expanding) empire were growing throughout the nineteenth century and remained strong right down to decolonization. This evidence adds weight to the view that the empire was indeed a substantial business operation. The second omission is the lack of a discussion of Britain’s informal empire. This is especially odd because Porter emphasizes the importance of the informal presence in arguing for the imperial character of the United States today, yet he says little about Britain’s influence in Latin America, the Ottoman Empire and China in the nineteenth century. Had the economic ties and the informal presence been inserted into his analysis, they would surely have brought some modification to the argument that the empire was a ‘much lesser affair than it is sometimes taken to have been’ (p. 22).

In emphasizing the weakness of Britain’s position in the period after the First World War, Porter appears to discount the revisionist work that has qualified the decline and fall thesis. The British revitalized the imperial mandate after 1918, mobilized new means of communication and control, strengthened economic ties though the Ottawa agreements and associated bilateral accords, made concessions to nationalists while retaining essential powers, and regained a good deal of their pre-war influence in South America, the Middle East and China. Moreover, power needs to be thought of as being relative as well as absolute. Measured in absolute terms, Britain had less power after the First World War than before (depending on what indices are selected), but in relative terms she was still ahead of her rivals. Germany and France suffered even more grievously during the war; the United States withdrew in the 1930s. On the eve of the Second World War, Britain was still the only truly global power, and after 1945 she mounted a second colonial occupation that succeeded in holding the empire together during the vital decade needed for post-war reconstruction.

With regard to the American side of his argument, Porter is surely correct in identifying the United States as being a fundamentally expansionist power (p. 65). This theme has generated an extensive literature that goes back at least to Turner’s classic study, The frontier in American history.Footnote ¹⁸ It is undoubtedly true, too, that westward expansion ‘displayed many common imperialist experiences’ (p. 66), being grasping, violent and racist. But the comparison with Britain stops at this point. Although the policy adopted by the United States endorsed imperialist means of expansion, the resulting polity was not an empire controlling colonial subjects, but a large, independent nation-state with a common citizenry (even if some citizens were for long treated as if they were subjects).Footnote ¹⁹

The results overseas were very different too. Britain acquired a huge formal empire; the United States did not. It is true that the United States participated in the new imperialism of the late nineteenth century, chiefly through its war with Spain, and acquired territories in the Caribbean and Pacific as a result, but these were of minor account and were not augmented subsequently by additions of any consequence. On the contrary, isolationism remained a strong influence on foreign policy, and constitutional restraints imposed barriers on territorial acquisition. It was hard for the United States to divide or devolve sovereignty, as the British did in the dominions. Acquired territories had either to be incorporated as states of the union or returned to nature. Any intermediate status was anomalous and rarely granted.Footnote ²⁰

Accordingly, the argument that the United States was (and is) a large imperial power rests almost entirely on the claim that it created an informal empire after 1945. Porter presents such a case, as others have done, but it is not made as easily as might be thought, given the visibility and extent of American power in the world. The central problem lies with the notion of informal empire, which historians have wrestled with for over half a century. We cannot now do without it, yet there are limits to what we can do with it. The United States had the power to shape the reconstruction of Europe after 1945, but its influence diminished as recovery progressed and European states began to reassert their independence. The massive military strength and associated political presence of the United States in Vietnam ought to have been sufficient to have created an empire there, informal or otherwise. The outcome, however, was a comprehensive defeat.

This reverse, combined with the continuing uncertainties of the Cold War and the seeming threat posed by the unanticipated rise of Japan, provided the context for the influential ‘declinist’ literature that appeared in the 1980s. Porter does not take these developments into account, and instead leaves readers with the impression that the triumphalism of the 1990s is a more faithful representation of the standing of the United States than the pessimism of the previous decade.Footnote ²¹ Current events, however, outpace even speedy historians, and the credibility of the declinists has now revived as the adverse consequences of imperialist policies in the Middle East have become apparent.

These observations suggest that the effective power of the United States may be more limited than Porter supposes. He is impressed, as are almost all other commentators, by the undoubted fact that the United States can call upon military resources far in excess of those commanded by the British in the nineteenth century.Footnote ²² On this basis, Porter concludes, as do many others, that the United States is a world power without parallel. The problem with this assessment is that the comparison with Britain is, in this instance, irrelevant. What matters is not whether the United States today has more (or less) military power than Britain had at her height but whether each power had or has the capacity to achieve its goals. On this measure the relativities do not clearly favour the United States. The large US military is organized to fight states, not shifting resistance movements and ‘terrorists’, still less abstract concepts like ‘evil’. Vietnam was a disaster; intervention in Lebanon and Somalia was unsuccessful; the occupation of Afghanistan and Iraq has devastated both countries but has not achieved its goals and is unlikely to do so; intimidation has not brought compliance from either North Korea or Iran. The British, it might be thought, did rather better at putting down some of the evils of their day, such as the slave trade and piracy.

Looked at from this perspective, the British Empire may have been weightier and the American empire lighter than Porter allows.Footnote ²³ Foreign policy was certainly supercharged after 9/11 but it has yet to produce a superempire and may not do so. Moreover, the American empire, if it is one, has yet to prove its durability. Porter emphasizes, correctly, the pervasive ideological basis of current American foreign policy. But this is changing. The neoconservatives have now lost much of their influence; advocates of an expanded, benign empire have fallen silent. The reaction to excessive idealism is reintroducing a measure of realism to foreign policy. In an age of globalization, this shift will not lead to disengagement from the wider world, but it may encourage the use of ‘soft’ power rather than ‘hard’ powerFootnote ²⁴ and a reversion to the exercise of informal influence, though without necessarily creating an informal empire.

From hyperpower to hype

Criticism, as every reviewer knows, flows easily; creativity, as every author knows, freezes quickly. This being so, Maier and Porter deserve unqualified appreciation for tackling large and complex subjects and the attendant difficulties raised by the use of key terms and comparisons. A consideration of definitions compels other historians to examine the foundations of their own thinking. Comparisons check the assumption that our own experience is the norm from which others deviate, and question the inference that deviation is a threat to our own values. In linking the record of the United States to imperial history, Maier and Porter have helped to turn the study of American history away from its predominantly insular orientation and to open imperial history to further comparative analysis.Footnote ²⁵ These are creative developments; they are also highly appropriate in an age of globalization, when borders of all kinds are being surmounted and reshaped.

Holistic terms and comparisons are scattered throughout all historical studies. Their importance suggests that they should be closely defined; practice indicates that they are often waved through with little scrutiny. Very broad definitions support broad conclusions and allow comparisons to be drawn from a wide variety of regions and eras. Their spaciousness is attractive, but their value is limited because conclusions drawn at a very high level of generality are unlikely to be illuminating. Poorly specified definitions, and the comparisons that accompany them, may also produce dubious results. It was this flaw that led to the downfall of the comparative ‘method’ formulated in the nineteenth century and exemplified in Toynbee’s monumental Study of History.Footnote ²⁶

The way around these hazards is to define key terms according to the purpose in hand, which in turn requires a clear statement of the problem to be investigated. Maier’s study suffers because it lacks a closely specified problem or an explicit hypothesis, and the wide-ranging historical evidence the book presents is tied too loosely to the issues at stake for its value to be fully realized. Porter’s book, on the other hand, has both a definition and a problem, and can be evaluated by judging the strength of the evidence presented in support of the central argument.

Even so, historical comparisons present formidable difficulties.Footnote ²⁷ Comparing like with like is a principle that can be applied more easily in distinguishing apples from pears than in categorizing empires. All empires must share some features if they are to retain the name, but what they share may be less significant than what separates them. This understanding, presumably, explains why the Venetian Empire is rarely, if ever, compared to the British Empire. The British and American empires, on the other hand, have more in common because they are both founded on capitalist nation-states. Nevertheless, the search for similarities still needs to take account of differences if the results of the comparison are to be robust. Historical comparisons that detach states or societies from their chronological location enable similarities and differences between particular features, such as military resources and ideology, to be closely observed. But they also run the risk of minimizing or even overlooking important shifts in the global context within which the comparison is set. The world of the mid-nineteenth century was very different from the world of the late twentieth century, not least because of changes brought about by imperialism. The former period favoured the creation and expansion of empires; the latter did not. From this perspective, it might be argued that the United States is a super-power but not a super-empire.

Their deep knowledge of history has restrained Maier and Porter from advancing over-confident predictions about the trajectory of the world’s latest ‘empire’. This ambition has driven a good deal of work on this theme by authors who have tried to discern the pattern of the future from an often-limited knowledge of the past. The teaching of Giambattista Vico, whose theory of comparative history founded the modern study of the subject, reminds us that the path of prediction is never smooth. Vico was optimistic in believing that society was travelling towards perfection, but realistic in supposing that it would never arrive. He formulated a stage theory of history whereby the age of beasts gave way to the age of gods, and the age of gods, in turn, to the age of heroes and the age of men. But he also recognized that each age was full of surprises, including the prospect of returning to a state of bestiality. Where man failed, only the hand of providence, the corrective of last resort, could right the course of history. These are salutary thoughts for policy-makers and intellectuals in dominant states who are easily beguiled by their temporary supremacy into believing that they know how to reshape the world, control the upheaval they instigate, and turn lead into gold.Footnote ²⁸