Adam Smith once opined that “the discovery of America, and . . . of a passage to the East Indies by the Cape of Good Hope, are the greatest and most important events recorded in the history of mankind.” Whatever their importance for human history, they were also pivotal moments in the history of international law.  The great voyages of discovery by Spain in the west and Portugal in the east not only inaugurated modern European imperialism and intercontinental trade, but also forced Europeans to think about the lands they “discovered” and the new peoples with whom they interacted in terms of legal relationships, oftentimes in novel ways.     

Portugal was the first of the two Iberian powers to strike out boldly on the high seas in the early fifteenth century. In 1434 a small fleet triumphed in sailing beyond Cape Bojador, an important headland in the western Sahara that many had theretofore considered the edge of the navigable ocean.  But this was not discovery for discovery’s sake.  The distance and difficulty of the overland spice route from Asia, via the Middle East to Venice and then beyond into Europe, resulted in price markups of up to two thousand percent.  For example, pepper and nutmeg were subject to such markups, suggesting lucrative trade opportunities by sea that even a lesser economist than Smith could perceive.  By 1498, Vasco de Gama successfully reached India by travelling around the southern tip of Africa. Although he returned to Lisbon with only half the ships with which he had set out, the value of the spices he brought back recouped the expedition’s cost by a factor of sixty!  King Manuel II, laying eyes on the precious cargo, exclaimed “it would seem that it is not we who have discovered them, but they who have discovered us.”

The Spanish, meanwhile, were relatively late to the game of discovery.  The kingdoms of Aragon and Castille, unified in 1469 with the marriage of King Ferdinand and Queen Isabella, had long been embroiled in the reconquista, the campaign to drive “Moors” or Muslims from Iberia.  In 1492 they vanquished Granada, the last Islamic kingdom on the peninsula.  Isabella, in part as an act of pious thanksgiving for the Christian victory, deigned to support the stratagem of a little-known but insistent Genoese cartographer and itinerant mariner, Christopher Columbus, to sail not east around Africa to the riches of Asia, like the Portuguese, but west across the open Atlantic.  Although Columbus was adamant until his death that the lands he discovered were islands off the coast of Asia (even more fantastically, he believed an earthly paradise, rather than a new continent, to be the source of the freshwater that flowed from the Orinoco River), others were quick to discern the true nature, and potential riches, of America.  

Portuguese and Spanish claims to this vast bounty and territory were almost immediately the subject of legal discussion.  In response to a petition by Ferdinand and shortly after Columbus returned from his first voyage, in 1493, Pope Alexander VI promulgated a series of bulls recognizing the title of the Spanish crown to the lands “as all you have discovered or are about to discover.” A year later, again with Rome’s blessing, Spain and Portugal signed a treaty in the town of Tordesillas that divided the world between them, at a line of longitude “370 leagues west of the Cape Verde Islands,” approximately 46°30’W.  The lands to the west went to Spain, in recognition of Columbus’ finds, and those to the east to Portugal, in theory including the entire coast on either side of the Cape of Good Hope, India, and also Brazil, to the coast of which Portuguese mariners soon strayed at the point where it is nearest Africa. Not surprisingly, the Alexandrine (Papal) Bulls and Treaty of Tordesillas were treated with contempt by other European powers, which later sought novel legal justifications for their own colonial activities.

There was, however, opposition much closer to home. Spanish title to the “New World,” backed by the Church, was based on the ancient Roman legal principle of res nullius, that unoccupied property being the common patrimony of humankind and subject to claim by the first to put it to use.  According to a thirteenth century Castilian legal code, “it rarely happens that new islands arise out of the sea.  But if this should happen and some new island appears, we say that it should belong to him who first settles it.”  Rarely indeed, until 1492!  But a number of Spanish theologians and jurists underscored that the continent and islands of America were inhabited by both primitive natives, who were easy to ignore, and complex civilizations like those of the Aztecs and Incas, which were not.  Thus, the Dominican friar Francisco de Vitoria, a theologian at the University of Salamanca, questioned the legality of Spanish claims in America.  In his famous work De Indis (1538), Vitoria argued that the Spanish merely possessed the right to travel and dwell in America, to trade with native Americans, and to spread the Gospel. He asserted that only if the Spanish were denied these rights (but not if natives refused the word of God) could they make war and thus formally acquire new lands, because “[i]t is lawful to meet force with force.”

Members of the “School of Salamanca,” the name given to the Thomist natural law movement that Vitoria founded, were, like their leader, motivated by a number of political considerations (limiting the pope’s jurisdiction in international affairs, for example, seemed sensible after His Holiness granted the Portuguese the Pacific Ocean in 1514) but also by the devastation visited upon native Americans by Europeans, most descriptively illustrated in Bartolome de Las Casas’ Brief Account of the Destruction of the Indies (1542).  On first arriving in America, Columbus had insisted that the natural docility of native Americans perfectly suited them to be slaves, but Queen Isabella, a devout Catholic, and the Pope himself determined instead that they were to be evangelized.  In the long term, however, the vast majority of native Americans were killed, most extensively by diseases such as smallpox, measles, and typhus: the population of the former Aztec Empire fell from twenty-five million in about 1520, to just one million in 1600.  To help repopulate the Americas, Europeans therefore looked to a population they had encountered earlier during the Age of Discovery, one that an earlier Pope, Nicholas V, had in 1455 granted King Alfonso V of Portugal the legal license to reduce to perpetual slavery—black Africans.