In 1978, the Estonian political scientist, historian, and politician Rein Taagepera published the first of three quantitative history articles on the “Size and Duration of Empires.” In the first, subtitled “Systematics of Size,” Taagepera made the case for three phases in world history, based on step-changes in the land areas of the largest empires. The first phase was from 2850 BCE until 500 BCE, the second from 500 BCE until 1600 CE, and the final one, 1600 CE until the present. Taagepera’s articles are foundational work. Although such quantitative approaches went somewhat out of fashion in the 1980s and 1990s, they have now returned to favor. One notable instance is the recent work of Peter Turchin, who, like Taagepera, was an exile from the communist East.

In Shadow Empires: An Alternative Imperial History, Thomas J. Barfield draws directly on the quantitative data compiled by Rein Taagepera and Peter Turchin. Like them, he is interested in formulating large-scale comparative theories about empires over the longue durée (long term). Although he does not explicitly frame it in relation to Taagepera’s work, his main focus is Taagepera’s middle phase—between circa 500 BCE and 1600 CE—when the largest empires were often in the region of five million square kilometers in land area and had populations of perhaps tens of millions of people. Barfield discusses more than a dozen empires from this middle period in detail, including Achaemenid Persia, Athens, Alexander and the Seleucids, Qin and Han China, the Xiongnu, Rome, Carolingian Francia, the Umayyad and Abbasid Caliphates, the Khazars, the Kievan Rus’, the Khitan Liao, Jurchen Jin, and the Mongols. He also treats three empires from circa 1600 to 1900 that were far larger than earlier formations, the Manchu Qing, Russian, and British empires, as well as the Holy Roman Empire, which was smaller but illustrates a distinctive pattern in post-Roman western Europe. In the final sections of his final chapter, Barfield turns briefly to the global reach of the United States of America, the Soviet Union, the People’s Republic of China, and the European Union, in the 20th and 21st centuries.

Therefore the chronological focus is mostly (but not exclusively) premodern, and geographically it is Eurasia, in which all the empires Barfield examines in detail had their centers. Barfield justifies these choices as a reframing of the way that we think historically about empire—a full understanding of empire should account not just for the Roman Empire in the Mediterranean and Europe, but also for the empires of the Middle East and China, and the steppes of Central Asia. As he puts it, “it is clear that the most enduring traditions of empire-building were not in the West but in China and Persia, where empires emerged earlier, lasted longer, and (most significantly) reemerged after periods of collapse, whereas Rome did not” (p. 8). For Barfield, Taagepera’s step-change in scale circa 500 BCE reflects something foundational—many subsequent polities adopted new technologies and governmental methods. Crucially, Barfield also argues, empires that formed on the peripheries of China, Iran, and Rome should be much more central to the world history of empire. In this way, Barfield’s book is also part of a wider return to a comparative history of empire that decenters the West and pays greater attention to the premodern world. Walter Scheidel’s 2019 Escape from Rome: The Failure of Empire and the Road to Prosperity and Ayçe Zarakol’s 2022 Before the West: The Rise and Fall of Eastern World Orders are two other examples of this trend.

Barfield’s distinctive contribution is that he proposes a comparative analytical framework that distinguishes between “primary” or “endogenous” empires and “secondary,” “exogenous,” or “shadow empires,” with the latter contingent and predatory upon the former. An endogenous empire’s elites acquire their resources through the conquest of neighboring polities and those territories’ subsequent incorporation into an imperial system. In contrast, an exogenous (or shadow) empire is symbiotic with or exploitative of neighboring polities, but often with no intention to permanently incorporate their lands. Barfield argues that these “shadow empires” are not only less well understood than their endogenous neighbors but also just as important for understanding the history of empire over the longue durée. The book shows this distinction to be an effective interpretive framework, revealing new patterns in the evolution of empires over the past 2,500 years.

Shadow Empires is a long-form treatment of an idea Barfield first outlined in his 2001 book chapter, “The Shadow Empires: Imperial State Formation along the Chinese-Nomad Frontier.” The book allows for the fuller illustration and development of this idea, with reference to detailed historical examples, grounded in wide reading of the literature on each. The shadow empires are further subcategorized in classifications that are articulated in the five middle chapters of the book—in turn: maritime empires (Athens and the British in India); steppe nomadic empires (the Xiongnu and the Mongols); vulture empires (the Khitan Liao and Jurchen Jin); vanquisher empires (Alexander and the Caliphate); empires of nostalgia (the Carolingians and the Holy Roman Empire); and vacuum empires (the Khazars, the Rus’, and Muscovy). These categories are “ideal types” (p. 7) in the Weberian sense—Barfield deploys them advisedly, on the basis that they have explanatory power, not to claim that any specific historical example exactly fits his templates.

Three of these five types are straightforwardly symbiotic with, or predatory upon, neighboring polities. Maritime empires are characterized by their use of naval force to control revenues, without seeking to control more territory than necessary for revenue acquisition. Similarly, the steppe nomadic empires were land empires that developed in tandem with the empires of China, dependent upon extracting wealth from the empires to their south. Both these types of empire could achieve “a favorable modus vivendi” (p. 152) with the neighboring powers, or, as with the British in India or the Mongols in Eurasia, they could transition from symbiosis or predation to direct, endogenous rule.

The much rarer vulture and vanquisher empires formed where groups peripheral to collapsing or otherwise vulnerable neighbors conquered them quickly, often within a generation or two, thereafter becoming endogenous empires themselves. The example most familiar to this reviewer is the Islamic Caliphate. Necessarily, Barfield is dependent on literature a few years short of the current state of the field. Therefore the question of the vulnerability of Rome, and especially Iran, in the wake of their war of 602–28 CE is somewhat glossed over, as is the importance of the Arabic-speaking pastoralists within their frontier territories, perhaps diminishing some of the early caliphate’s more vulture-like (as opposed to vanquisher) characteristics. So too is the extent to which the gradual formation of the empire was integral to the postconquest emergence of both Arab and Muslim (and Sunni and Shiʿi) identities, as shown in recent work by Fred Donner, Illka Lindstedt, and Peter Webb. There are further questions to ask about the history of the early Islamic tax system, as explored by Petra Sijpesteijn and Marie Legendre. The idea of a Persian restoration in Abbasid times is also schematic and does not take full account of the specific groups that shaped Abbasid rule, as in works by Saleh Said Agha, Parvaneh Pourshariati, and Étienne de la Vaissière. However, such limitations do not obviate the overall interpretation of the Islamic Caliphate’s formation as an exceptional episode of rapid conquest by groups peripheral to the empires they replaced, which led in turn to the formation of new endogenous empires.

The other two types are shadows in different senses. The vacuum empire is presented specifically with reference to Eastern Europe and northern Eurasia. From the 7th century CE, new imperial polities expanded into the sparsely inhabited—and initially near-stateless—forests, steppe, and tundra of eastern Europe and Russia, eventually meeting, over one thousand years later, with the Manchu Qing empire and so closing down the possibility for further steppe nomadic empires to form.

Empires of nostalgia are entirely different. By this, Barfield means the invocation of the idea of the Roman Empire by the Carolingian Franks and then the Holy Roman Empire. This chapter feels a little out place. Elsewhere, the book focuses more on organizational power (to borrow a term from the historical sociologist Michael Mann, whose work is not cited) than on ideology; for example, nostalgia for the Caliphate or Chinese ideas about unity and stability, which are mentioned but not developed, might be explored further: the universalist claims of Islam mirror those of post-Roman imperial Christianity and are at least as important in the legitimation of imperial formations. Chinese ideas about the “mandate of heaven” might be further compared with these monotheist traditions’ potential as imperial ideologies.

In his final chapter, Barfield turns to the 19th and 20th centuries. The rise of capitalism and the repeated technological revolutions of the industrial age rendered the old empires vulnerable, with none surviving World War I intact. Indeed, Barfield is skeptical that “empire” is a useful category to describe the “great powers” from the period after the watershed of the early 1900s. However, he proposes that 20th-century and 21st-century global political structures borrowed “to a surprising extent” the “tools developed by now-extinct empires. . . particularly shadow ones” (p. 302). For example, he sees parallels with the strategies of past maritime empires in the United States presiding over a world economic system that benefits it above other polities, and in its maintenance of military outposts in the lands of its allies; modern post-Soviet Russia Barfield sees as returning to the expansionist policies of early modern times; and in the European Union, Barfield finds some echoes of the Holy Roman Empire, albeit—exceptionally—in a voluntary association, and a secular one.

Ultimately, it is the explanatory power of Barfield’s typology that determines the value of the book. Although specialists will no doubt find oversights—such as those noted regarding the Caliphate—the main claims remain convincing. What is most compelling is the emphasis on the distinctive patterns of the two thousand years spanning the second half of the first millennium BCE and the first millennium and a half CE. At the beginning of this period, modes of imperial practice were established in China, Iran, and Rome that would last for centuries in the case of China and Iran, whereas Rome would leave a long shadow of nostalgia. Moreover, the steppes, highlands, and forests to the south and north of these endogenous empires generated distinctive, exogenous, forms of empire, which formed in tandem with their endogenous neighbors. The greater attention paid to the steppe nomad empires and to the Caliphate shifts the perspective. It makes the patterns of the Roman and post-Roman West look like the exception rather than the rule and gives much greater prominence to nomadic pastoralists’ political structures and the critical role of interactions between polities in generating new formations.

In these observations, Barfield’s book is a sort of counterpart to Walter Scheidel’s Escape from Rome. Scheidel argues that it was precisely the absence of successful empire in the politically fragmented and competitive environment of post-Roman Europe that was the incubator for the emergence of the innovative elites who brought about the transformative developments of the last four hundred years. Indeed, it is perhaps its treatment of these past four hundred years that is the weakest aspect of Barfield’s book—the imperial polities that developed in this period were exceptional for their scale but also, even before the fossil fuel revolution of the 19th century, for their use of new technologies and new cultural forms (on both points, see Taagepera). These included the instruments of finance, credit, and the limited company, combined with the revival of slavery in its new, transatlantic iteration. Meanwhile, in the East, distinctive fusions of Perso-Islamic and Turco-Mongol political culture developed in the Ottoman, Safavid, and Mughal empires, whose scale, duration, and extractive power were unprecedented. These developments are remarked upon by Barfield. However, the steep and lasting uptick in Taagepera’s graph circa 1600, the subsequent demographic collapse of the indigenous peoples in the “new” world between the 16th and 20th centuries, and the power of capitalism to concentrate unprecedented wealth in the hands of European elites, both in Europe and in their colonies and former colonies, perhaps demand more detailed discussion than they are accorded here. Likewise, the universalist claims of early modern and modern religious traditions (and their modern secular counterparts) might merit more attention.

That said, the era after 1600 is not the book’s main focus. About two-thirds of Barfield’s examples are empires that flourished before 1000 CE. The typology of empires and the dynamics between them in these formative centuries at the end of antiquity, together with the detailed narratives that support it, are the major contributions of the book. The scale, ambition, and erudition are enormously impressive, and the well-researched and diverse imperial histories are a useful resource in themselves, as well as being presented in a way that recognizes the limits of the “ideal types” with which Barfield is working. Shadow Empires is a significant intervention in contemporary reckonings with empire and imperialism—reckonings that are taking place as the post-1945 world order is shaken by new demographic, technological, and environmental forces.