This chapter examines the role of authority in public international law, based on the preceding discussion of authority and legitimacy in the context of exercises of power. Although there is a source of power, if not authority, at the domestic level in the form of government, this does not automatically transfer to the international level. This is primarily because the international system exists without a central authority. The question automatically arises of who ought to be able to make such rules, and whether the requirement for the exercise of autonomy is still as critical as it would be at the domestic level. The discussion is based on an analysis of foundational texts, exploring the ideas of authority at the international level expounded by Grotius and Vitoria, before moving on to work by more recent authors.

This chapter explores the link between international law’s long-standing doctrinal commitment to commerce and its inability to act decisively on behalf of the environment. One of the fundamental rights the early authors of jus gentium discovered was the right to engage in commerce. Vitoria, Gentili, and Grotius each drew on a providentialist theory of commerce. The doctrine held that Providence distributed scarcity and plenty across the Earth so that people could not be self-sufficient but would need to go in search of one another in order to acquire what they lacked. Commerce imagined in its pure form of reciprocal, mutually beneficial exchange would be the means to bring separated mankind to friendship. The embrace of such doctrine by early exponents of the law of nations, carried forward by Vattel, set the stage for international law’s longstanding commitment to international commerce, viewed as a virtuous activity that tends to the common good. An additional legacy was the view of nature as commodity. The providentialist doctrine of commerce remains embedded in international law and hobbles its ability to protect the natural environment.

Grotius recast Aristotelian theories of human sociability in terms of self-preservation.Religious war in Europe had undermined the Thomist notion of mutual human affection as a basis for society.If society was established by the need to survive, then justice, which maintained society, must be understood in terms of its contribution to that necessity.Grotius therefore resolved the Ancient Roman and Greek problem of how to reconcile justice and expedience by reinterpreting justice in terms of expedience.For an individual, or state, to act out of self-preservation was necessarily just.His fusion of justice and expedience was one reason he was insistent upon distancing his thought from the Academic Sceptics, such as Carneades, who argued that there was no such thing as justice and that all moral action was expedient.For Grotius, part of the law of self-preservation was the necessity for individuals to secure the means for self-preservation and this meant that the acquisition of property, and trade, were central parts of that process.These principles applied also to the artificial person of the state which found itself in competition for survival with other states.The expansion of the state was therefore justifiable for its preservation.Indeed, following this reasoning, empire effectively became a necessity, and an inevitability, for the survival of European states.

In the utterly religious world of 16th-century Europe, the most important legal authority was power over consciences. At a time of confessional crisis, imperial theologians from Salamanca lent their assistance to the Counter-Reformation by employing the amalgam of a moral theology concentrating on individual confession and Roman legal principles they found in the works of Thomas Aquinas. These would offer the means to instruct Christians on what attitude to adopt towards the treatment of the indigenous population of the New World and what to think of the incessant wars between Christian princes and the expansion of a commercial ethic that was hard to fit with old moral theology.

This chapter examines the early emergence of civilian protection norms in medieval Europe and traces their development in the religious and secular strands of just war theory. It argues that the Peace of God played social movement in medieval Europe played a key role in the emergence of the principle of civilian immunity. Second, it shows that the theory set forth in Chapter 2 provides a useful account of how the principle of civilian immunity arose in medieval Europe and why it persisted from the medieval period through the Enlightenment. Throughout, it examines the arguments of key just war theorists and international lawyers, including Augustine, Aquinas, Vitoria, Suarez, Grotius, and Vattel.

The 1648 Peace of Westphalia typifies the “modern” starting point of state sovereignty and humanitarian intervention within conventional historical treatments of International Relations (IR) theory. The treaties ending the Thirty Years’ War signaled the dawn of an international society after medieval Latin Christendom with new diplomatic arrangements that assigned legitimate autonomy to specific European states independent of Roman imperial and papal authorities. The ideological archetypes of Westphalia for IR theory during the twentieth century were contemporaries, Thomas Hobbes (1588–1679) the realist and Hugo Grotius (1583–1645) the rationalist. Each of them powerfully envisioned a modern form of international relations: Hobbes accented sovereign political independence and international anarchy between states whereas Grotius affirmed a worldwide association of states absent a global authority yet still regulated by norms of universal law to justify war and intervention.

What to focus on in an intellectual history of ius gentium et naturae for a volume on the relations between international law and Christianities? For centuries, (international) law and Christian theology maintained intensive and complex relations, which it is impossible to do justice to within the scope of this chapter. With the more recent “turn to history” in international legal scholarship, discussions of the relationship between ius gentium et naturae and Christianity generally center on secularization and/or empire. For obvious reasons both sets of histories deal with early modernity – the time that the so-called Respublica Christiana or Holy Roman Empire was profoundly affected by Reformations, gradually fragmented, and religious and theological fights were part of the politics of the newly emerging European nation-states.

Beginning with their Master General, Cajetan, Spanish Dominicans precipitated and outlined the theological parameters for thinking about infidel dominium of peoples outside Europe as a matter of restitution and salvation. This pairing of justice and evangelization opposed the long-standing idea and practice of missionary war in the theocratic conception of world order that linked conquest and preaching and was being defended by Spanish theocratic royalists and the “modern” theology of John Mair. In 1535, after Francisco Pizarro’s conquest of the Inca, Francisco de Vitoria, Domingo Soto, and Bartolomé de las Casas drew from the inspirational example of the first Dominican missionaries to the New World and began formulating an unprecedented scholastic theological conception of world order. Appealing to Scripture, the apostolic tradition, Thomistic moral theology, Roman law, and canon law, their account of world order contained a discourse of natural subjective rights for all persons made in the divine image, attentive to restoring the injustices suffered by the Amerindians of the New World. The originality of the Spanish Dominicans, with Vitoria’s Relectio de Indis at the center, lay in their articulation of infidel rights over and against unjust European claims of expansionary religious wars waged by emperors and popes alike.

In view of seventeenth-century Protestant humanist transformations, this concluding chapter returns to the Spanish Dominicans and their scholastic-juristic view on the law of nations as a normative resource for thinking about international society. Their Thomistic attention to the rationality of the universal law of nations as positive human law enabled political recognition of non-European polities, the lawful occupants of the Indies. This contrasted with an imperial-humanist jurisprudence that provincialized natural law and the law of nations under European civilizational hierarchy to justify dispossession of inferior peoples. The chapter especially charts the evolution of Las Casas’s thinking through his interaction with the theologians at Salamanca. His eclectic synthesis of Thomistic theology, canon law, Roman law, and humanism to buttress indigenous occupation exemplified a radical scholastic brand of legal humanism that complicates static ideological categories in the history of international legal thought. By placing Las Casas in conversation with his Dominican confreres, a normative view of the law of nations grounded in Christian theological convictions emerges. It accounts for the independence and interdependence of all peoples, and the indispensable role of justice and solidarity in promoting world order under a Christian ethic of loving one’s neighbors.