Magnus Ryan reverses the standard story of the development of Roman Law: that a law declared universal and eternal by the Emperor Justinian, and accepted as such by the medieval lawyers, was finally ‘historicized’ in the sixteenth century by the French historical school of Humanist jurists. On the contrary, Ryan argues, the understanding of Roman Law held by medieval jurists down to Bartolus was strictly historical, premised on the assumption that the kingdoms and cities of medieval Europe were continuous with the Roman Empire, their authority derived from the same ‘lex regia’ by which the emperors had been granted their authority by the Roman people. The first breach in this assumption of historical continuity appears to be made in the fifteenth century, when similar transfers of authority were identified as taking place independently; and in the sixteenth century Protestant resistance theorists began to claim that original popular authority was a universal principle, exemplified severally in the original, ‘ancient’ constitutions of individual kingdoms (such as France). It was by abandoning the premise of historical continuity with Rome, in other words, that Roman Law was made ‘universal’.

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.