In relation to international law slavery has undergone dramatic alterations. It was one of the first legally defined statuses of human relationships to be justified in a code of laws as a universal condition. Only after two millennia did it come under sustained juridical and political attack as an institution. The first element of the institution to be targeted for suppression was the transoceanic slave trade. After becoming the focus of a sustained civil and political mobilization, its abolition became a global crusade. Slave trading was also the first economic enterprise to be formally condemned in an international treaty as repugnant to the principles of humanity and universal morality (1815). Its practitioners were also the first category of law breakers to have their cases adjudicated before international courts. In the twentieth century, enslavement was also among the first activities to be prosecuted in the Nuremberg tribunals (1945) as a ‘crime against humanity’. Probably in token of the long history of its suppression, the practice of enslavement figured as the first specific violation of human rights listed in the Universal Declaration of Human Rights (1948) and in international human rights instrument thereafter. Slavery’s position as a consensually condemned condition ensured that many other human rights campaigners would frequently endeavor to designate their targets for criminalization as slave-like conditions.
Slavery’s salience in recorded history derives primarily from its ubiquity and antiquity. In various forms it was identifiable in every continent of the globe. It appeared to reach back to the very origins of humanity. As an English court recognized at the beginning of the nineteenth century, personal slavery seemed ‘coeval with the earliest history of mankind’. It was found in the ‘earliest records of the human race’, and was embedded in the traditions of the ‘most polished’ peoples of classical civilization. Above all, in legal history it was an integral component of the most prestigious and durable juridical legacy of antiquity—Roman civil law. In that legal code slavery was given universal status. Roman juristic references to slavery being contra naturam ware immediately followed by the observation that it was an ‘institution of the ius gentium (law common to all peoples) and what natural reason prescribed for all men’.1 Although not incorporated in this legal definition, warfare and trade always remained the privileged methods for acquiring and distributing slaves. That conquest entailed the right to kill or to spare and dispose of the conquered remained at the heart of the implicit rationale for enslavement.
During the medieval period the boundaries of enslavability gradually came to be restricted by religious affiliation, but the enslavement of infidels in a just war offered ample scope for the continuation of the institution. In the case of captives from abroad, it was less important to inquire whether a person had been enslaved legitimately. From the standpoint of Roman law, the original status of an imported captive was defined by the ius civile of another state. This perspective was to inform European attitudes towards the status of Africans later transported to Europe and the Americas.2 In the Mediterranean, sub-Saharan Africa and central Asia, enslavement and the slave trade continued unabated in the early modern world.
The shift away from the premise of the universality and ubiquity of the institution began in Europe in areas located at the greatest distance from the Mediterranean zone of intermittent warfare and violent contact between Christian, Muslim and the non-monotheistic regions of Africa and Eurasia. In sixteenth-century northwestern Europe, slavery had yielded to regimes of contractual systems of labor. Encouraged by the expansion of medieval European urban notions of ‘free air’, juridical commentaries began to take note of the absence of slaves within their polities. Whether attributed to communal, royal, or religious inspiration, English, Dutch, and French jurists and communal governments claimed that as soon as slaves reached the soil or breathed the air of their nations they became as free of their condition as their masters.3
Strengthening this notion was the observation that, in contrast to antiquity, Christian nations had abandoned the principle that all civilian populations or prisoners of war were at the disposal of warring neighbors. Nevertheless, these notions of free soil and unenslavability were regarded as peculiar local innovations. For those engaged in developing international law the legitimacy of enslaving non-Christians ‘beyond the line’ of Christian Europe remained largely intact. This was especially easy for Iberian commentators on European overseas expansion and the transatlantic slave trade after 1450. In the Portuguese and Spanish empires there was no institutional discontinuity between their metropolitan and overseas colonies. Located at the frontier of interreligious warfare and mutual enslavement, the legitimacy of enslavability remained as firmly entrenched as the institution itself.
The Portuguese pioneers of the African slave trade to Europe and the Americas therefore represented Portuguese–African relations in terms of ongoing states of religious war. One fundamental principle of Roman civil law, inflected by canon law, held that captives in a just war offered a prima facie4 justification for enslavement. From the standpoint of civil law the status of captives purchased from abroad had already been determined. As the Portuguese expanded their explorations along the African coast, its inhabitants were seamlessly conflated with Saracens. As early as 1452 the Portuguese monarch gained Papal authorization for the ‘full and free permission to invade, search out, capture and subjugate the Saracens and pagans and any other unbelievers and enemies of Christ wherever they may be … and to reduce their persons to perpetual slavery’ for purposes of conversion.5 The fact that the Portuguese were in no position to invade Africa on a large scale underlay their emphasis on slave trading as the best available means for the conversion and salvation of Africans. From the Portuguese legal perspective, African policies of enslavement and sale thus constituted an integral part of the ius gentium.6
The transatlantic slave trade and its judicial legitimacy in the Americas was integrally related to the fact of Africa’s initial independence vis-à-vis Europe. The contrast with the Spanish policy towards the enslavement of Native American populations is striking. The conquistadors’ rapid domination of the most densely populated areas of the Americas, combined with the enormous mortality wrought by disease and exploitation, led a number of the Spanish clergy to denounce the enslavement of the Indians. The monarchy was induced to prohibit the further enslavement of Amerindians who voluntarily surrendered to Spanish domination. Under the usual terms of just war principles the only loophole in the prohibition occurred when a native population refused to accept the demand for submission and conversion. Thereafter enslavement continued only at the unconquered peripheries of the New World empires. As the transatlantic slave trade increased by more than tenfold between the mid-sixteenth and the early nineteenth century, there were only minor challenges to the legitimacy of slavery in the Iberian empires. There was never a public debate over the legitimacy of the African slave trade nor over an institution that legally existed in every part of the Spanish and Portuguese empire.7
Even north of Iberia, where the institution had vanished long before the launching of northern European overseas colonial ventures, political, legal and religious authorities offered no sustained opposition to overseas slaving or slave-holding. To rationalize this practice with their metropolitan ‘freedom principle’ these polities developed dual legal systems regarding the institution. Following the Portuguese example, the French monarchy formally sanctioned French slaving for purposes of conversion. Lacking an indigenous metropolitan slave code, the French monarchy created new colonial Black Codes. Slavery was renewed ‘beyond the line’ of metropolitan Europe. In Paris, a ‘Court of Conscience’ at the Sorbonne ruled that nothing in the Bible, the canon law or the civil law’s ius gentium prohibited the legitimate ownership of slaves.8 The premise of new needs for new settlements ‘beyond the line’ also prevailed elsewhere in northwestern Europe. In the Dutch and British empires, charters were offered to colonizing or trade companies endowing them with powers to formulate legal codes appropriate to their overseas situations. In England, an early legal formula (1584) allowed colonies ‘in remote, heathen and barbarous lands’ to make particular laws and statutes ‘agreeable to the laws of England’.9 All British governments during two subsequent centuries found slavery and the slave trade within in all of their dominions to be quite agreeable.
Early modern European commentators on the law of nations appear to have regarded the historical development of overseas slave systems as relatively insignificant to their concerns. The traditional categories of the civil law weighed far more heavily in their meditations. Echoing their medieval predecessors, slavery retained its traditional place as an integral and consensual element of the law of nations. Slavery was still in conformity with natural reason. It was still logically derived from the quasi-universal phenomena of war, captivity or poverty. Major commentators, including Balthazar Ayala, Cornelius van Bynkershoek, Hugo Grotius, and Samuel von Puffendorf, all agreed that the law of nations sanctioned slavery. Sir Thomas More considered slavery as an integral part of any society and in his Utopia (1516) he assumed that every household would have slaves, either imported from another country or local residents convicted of crimes. Similarly, the English liberation philosopher, John Locke provided for slavery in his draft of the Fundamental Constitution of Carolina (1669) and his two Treatises on Government (1690) both made room for the right of enslavement. The very nature of war still gave victors the power of life or death, potentially attenuated by enslavement. Intra-European restraints on exercising the power of enslavement were noted as a fortunate exception to the general rule that slavery remained integral to the law of nations. If the institution could be limited or attenuated by municipal law it still remained part of the world’s rational legal order.10
Early modern jurists did not remain attached to the prescriptions of ancient civil law solely in deference to tradition. The Roman law of slavery contained discussions of property law that were of considerable value to early modern commercial societies in the area of damages: if your property—your slave—caused harm, what was the extent of liability of a slave owner? In Roman law the head of the household (paterfamilias) was responsible for harm caused by dependents of his household for damages to others’ property. However, the owner retained the option of surrendering his slave in lieu of the monetary value of the injury; ‘noxal surrender’ meant that the master’s liability was limited to the value of the slave.11
From this, early modern commentators developed the idea that the liability of the property owner need not exceed the value of the property that occasioned the damage. It was unjust for the owner to be accountable beyond that limit. In this way the Roman law special provision for limited liability on slaves was extended to subordinate mercantile agents in general, against the prior prescription of Roman commercial law. In the initial revised interpretation, Dutch shipowners became responsible to creditors only for the value of the ship and its equipment, not for debts and damages accrued by captains. The principle was soon extended to cover any debts incurred by agents managing a merchant’s property. The principle of limited liability was established, regardless of the legal status of the agent.
The shift occurs so seamlessly because of the casual shift between property and persons in discussions of the law of nations as applied to conquered enemies. Hugo Grotius began his discussion of the laws of war as applied to belligerents by noting that what applied to the status of conquered things applied equally to persons. For Bynkershoek, even if enslavement in Europe had fallen into ‘disuse among Christians’:
we might still make use of it, if we so desire, and … the Dutch usually sell as slaves to the Spanish the people of Algiers, Tunis, and Tripoli … that they capture, for the Dutch do not use slaves except in Asia, Africa, and America. Indeed in 1661 and again in 1664 the States-General ordered their admiral to sell into slavery all the pirates he should take.12
If any of them was significantly influenced by the expansion of slavery and the slave trade in the Atlantic world they paid little attention to this new development in world history. Here the contrast between the lawyers’ treatment of slavery and piracy is striking. In no other aspect of early modern international law can the domination of antiquity be seen as in the comparative treatment of slavery and piracy. The civil law tradition unequivocally declared that pirates were hostis humani generis—common enemies of the human race. Piracy was designated without hesitation as an affront to the consensual law of nations. Its practitioners could be hung on the gibbet by the subjects of any ruler who seized them.13
Those who had to deal with the maritime aspects of international law could not so easily elude the increasing involvement of Europe in the slave trade. Charles Malloy’s De Jure Maritimo et Navali (1682) still confidently assumed that slavery was a general if not quite universal institution. Under certain conditions, he reiterated, enslavement was not repugnant to ‘natural justice by covenant [voluntary] or by “Transgression” [unvoluntary]’. European princes had universally agreed (the consensual requisite) ‘to esteem the words, Slave, Bondsman or Villain as barbarous’. In England, Trover could not be maintained even for a ‘More or other Indian’. Yet Englishmen abroad on the Atlantic and in the New World traded in servitude. ‘Beyond the line’ came to the rescue to rationalize the difference. Natural and mathematical laws had more certitude than civil law, and human activities were subjected to different ‘certitudes’ in different latitudes.14 It was not only the legal tradition but the reality of slavery that weighed upon lawyers and philosophers in considering the ubiquity of slavery in human society. From a global perspective, Europe’s rulers appeared as committed to perpetuating bondage on the eve of the American Revolution as they had been when the Portuguese purchased their first slaves on the coast of Africa three centuries earlier. In 1772, Arthur Young, a political arithmetician, offered a bird’s eye view of bondage in global perspective. Young estimated that of the earth’s 775 million inhabitants, all but 33 million could be classified as unfree. That same year, in the court of Chief Justice Lord Mansfield, the same point was reiterated by lawyer Francis Hargrave, pleading on behalf of the black servant James Somerset. In this landmark case Hargrave opened with a warning to the court and his countrymen that if the right of slavery was recognized in England, slavery ‘with its horrid train of evils’ would invade their island, ‘not only from our colonies and those of other European nations, but from Poland, Russia, Spain and Turkey, from the coast of Barbary, from the Western and Eastern coasts of Africa, from every part of the world, where it still continues to torment and dishonor the human species’.15 As Adam Smith warned his law students at Glasgow, they were not to be deceived by the absence of slavery in their one small corner of the globe. Slavery was to be found on every continent, and was likely to endure for ages, if not forever.16
In the half century after Smith’s lectures a new phenomenon intruded itself into the development of international law on slavery. For the first time antislavery became the policy of a sovereign nation, one which also happened to be the strongest economic, naval and international diplomatic power on the face of the earth. While attacks on slavery were launched almost simultaneously on both sides of the Atlantic (in the United States, Great Britain, and France), the British variant became and remained the largest, the longest, and the most indispensable agent of change. In America, antislavery was muted by the overriding fact that a significant component of the new federation was dominated by slaveholders. In France, the fledgling abolitionist movement was overtaken and superseded by the largest and most successful slave revolution in history. However, the declaration of slave emancipation throughout the French empire in 1794 was followed by the restoration of French slavery by Napoleon in 1802. By the second quarter of the nineteenth century the United States and France ironically became the two nations that most fiercely resisted the internationalization of abolitionism.17