Francisco de Vitoria, Statue before San Esteban, Salamanca

A noted scholar, he was publicly consulted by Charles V, Holy Roman Emperor and King of Spain. He worked to limit the type of power the Spanish Empire imposed on the Native Peoples. He said, "The upshot of all the preceding is this, then, that the aborigines undoubtedly had true dominion in both public and private matters, just like Christians, and that neither their princes nor private persons could be despoiled of their property on the ground of their not being true owners."[7] Vitoria denied that the native peoples could be understood as slaves by nature in Aristotelian terms.[8] He adopted from Aquinas the Roman law concept of ius gentium ("the law of nations"). His defense of American Indians was based on a Scholastic understanding of the intrinsic dignity of man, a dignity he found being violated by Spain's policies in the New World.

In three lectures (relectiones) held between 1537 and 1539 Vitoria concluded that the Indians were rightful owners of their property and that their chiefs validly exercised jurisdiction over their tribes. This had already been the position of Palacios Rubios. Neither the pope nor Charles V had a rightful claim over Indian lives or property. No violent action could be taken against them, nor could their lands or property be seized, unless the Indians had caused harm or injury to the Spanish by violating the latter's lawful rights.[2]

A supporter of the just war theory, in De iure belli Francisco pointed out that the underlying predicate conditions for a "just war" were "wholly lacking in the Indies".[9] The only area where he saw justification for Spanish intervention in native affairs was to protect victims seized for human sacrifice, and because of the inherent human dignity of the victims themselves—whose rights were being violated and thus in need of defense.[9]

Thomas E. Woods goes on to describe how some wished to argue that the natives lacked reason, but the evidence was against this because the natives had obvious customs, laws, and a form of government.[1]

The Spaniards were in the practice of invoking in their American conquests the so-called "Requerimiento", a document read to the Indians before the commencement of any hostilities. The "Requerimiento", declared the universal authority of the Pope, and the authority the Spanish monarchs had received from the Pope over this part of the New World for the purpose of colonizing and evangelizing it. The Indians had to accept the sovereignty of the Spanish monarchs or be compelled to submit by force. Vitoria denied the legitimacy of this document.[4]

His works are known only from his lecture notes, as he has published nothing in his lifetime. Nevertheless, his influence such as that on the Dutch legal philosopher Hugo Grotius was significant.[10] Relectiones XII Theologicae in duo libros distinctae was published posthumously (Antwerp, 1604).[11]

Francisco de Vitoria's writings have been interpreted by various scholars to support contrary policies.[12] Antony Anghie and others argue that Vitoria's humanitarianism legitimized conquest.[13]