This latest book by Anthony Pagden offers fascinating insights into the role that European imperial expansion played in the development of international law. It is based in large part on a number of previously published, though extensively revised, articles and papers, but it reflects a much larger body of Pagden’s work on the political and legal theory of empire and its importance in the history of European political thought.

The “burdens of empire,” on which the book focuses, refer to a centuries-long effort by a multitude of scholars to provide legal justification for European empires. This effort began with the Spanish conquests in the Americas and, specifically, with the problem of how to uphold Spain’s claim that its wars of occupation and dispossession were “just wars.” With this, scholars found themselves confronted with a larger “theoretical problem:” the need to create a universal law which could be applied to all peoples, and which could provide, as well, for “the extinction of the sovereignty of others” (p. 79).

Pagden’s account of these efforts begins in 1539 with the public lecture, entitled De Indis (“On the Indies,” or “American Indians”), which was delivered in January of that year by the prime chair of Theology at the University of Salamanca, Francisco de Vitoria (c. 1483–1546).

However, the real foundation of his account is the Spanish conquest of the Americas, beginning in 1492. Spain’s conquests in the Americas, Pagden tells us, caused the Spanish monarchy “considerable legal anxiety” (p. 56). Not only did its brutal conquest of the Amerindians challenge assumptions about the nature of sovereignty and prevailing notions of morality and right, the word “conquest” itself, which denotes an offense, conferred upon the Amerindians the right to wage wars of defense (“just wars”) against Spain. The Roman Empire, which was the key referent and model for Western European imperial powers, claimed that its wars of “conquest” were not fought for personal gain or glory, but were “just wars.” Spain sought to make the same claim, but on what grounds? For a war to be just it had to begin as a war of defense, either on behalf of oneself or of one’s allies and clients. But Cicero had argued that it could also “be waged against those who are believed to have offended not merely an individual or state but also humanity itself by violating the law of nature” (p. 57). Thus, the attempt to uphold Spanish conquests in the Americas focused on Roman legal codes and an “extensive reexamination, and sometimes reworking, of whole areas of the legal systems of early-modern Europe.” It was this effort that would shape the nature of what, in 1780, Jeremy Bentham would call “international law.”

Moral and legal arguments justifying or opposing Spanish conquests in the Americas set in motion a larger debate among theologians, moral and political philosophers, jurists, and public intellectuals about the nature and legitimacy, not only of European empires, but of empires everywhere. Ancient Rome’s conception of empire as an “extended polity based on a body of law” (p. 3), and the great codes of Roman Law, provided the basis for this debate.

Rome, like all empires, depended for its survival on its ability to win over the peoples who came under its rule. It was for this purpose that Rome extended to the conquered peoples of its empire something which, it claimed, all peoples should desire: membership in the Roman civitas (a system of legal rights and duties). The Roman civitas relied on a system of Roman civil law to govern the citizens of the empire, and on a system of laws—the ius gentium (“law of nations”)—to regulate the relationship between Roman citizens and foreign peoples (gentes). In the sixth century, the Justinian Code extended the ius gentium by conceiving it as an aspect of natural law, thus making it the basis for a law which could be applied to relations among all peoples. It was natural law and, more specifically, this late Roman understanding of the law of nations as a secondary natural law that became the focus of attempts to justify and regulate empire and colonization until the end of the eighteenth century.

All three of the jurists who are considered to be the “fathers of international law,” Francisco de Vitoria, Alberico Gentili, and Hugo Grotius, attempted to re-work the Roman law of nations to create a legitimate basis for imperial expansion. Vitoria’s address, De Indis, was the earliest and most influential contribution to this attempt. His concern had been to show that the Amerindians deserved to lose their sovereignty because they had violated the law of nations. While Vitoria had conceived of the law of nations as a consensual positive version of natural law and thus changeable, the Italian jurist, Alberico Gentili (1552–1608), conceived of its content as identical with that of the law of nature and so in no need of further development (p. 92). For Gentili, this implied that, since the violation of natural law was a threat to all mankind, states had a duty to punish violators and a right to dominium over persons and moveable goods acquired in these wars. Hugo Grotius (1583–1645) argued that, since the law of nations could only have its basis in the customs of the most civilized nations, attempts by those states to ensure that all peoples of the world had access to those customs was morally justified. This began a tradition that, in the nineteenth century, culminated with the conception of a world divided into “civilized nations” who are governed by international law, and all the rest who are not (p. 93).

By the nineteenth century, the natural law tradition had come to an end, but it returned in the twentieth century in the Universal Declaration of Human Rights of 1948, which embodied an appeal for the rights of the individual. This is where Pagden ends his account, leaving us to ponder the irony that, while international law was developed by Europeans to serve European imperial expansion, its inclusion of rights that later would become “human rights” means that, despite its imperial origins, it was ultimately successful in achieving something that no other understanding of the law had achieved—the creation of a “universal conception of the person” (p. 256).

Pagden’s account offers an angle of vision that reveals under-explored dimensions and connections of international law, history, and political thought. It should be of particular interest to International Relations scholars involved in debates about international norms—those relating to diplomacy, the laws of war, sovereignty, international law, and international organisation—that are the basis for modern international relations, and the normative implications of universalising them.

Though it lies outside the remit of this richly detailed intellectual history, it would have been interesting to understand how this history connects with broader developments, including the larger Eurasian expansionism of which European imperialism formed a part, and the impact that European expansion into the world ruled by Islamic and other established cultures had on debates in Europe. Pagden is persuasive in showing that imperialism formed the context for the development of international law, but the context for both was the expansion of capitalism, the emergence of industrial production, and anxieties about social cohesion and revolution this generated throughout the world. It would be interesting to know something about how these were connected to empire and the development of international law. While these connections might provide a more complete picture, Pagden’s fascinating account of the debate which Europe’s imperial project set in motion among Europeans, and its impact on the development of international law, provides an extraordinarily strong foundation on which to build.