Throughout the history of international law, there have been diverse interpretations about the nature of Francisco de Vitoria’s ideas. Among the most influential are Critical Legal Studies’ views. According to them, Francisco de Vitoria was the founder of an international legal discourse that was ethnocentric, pro-colonial and imperialistic. As an original contribution to the study of international legal ideas and contrary to CLS interpretations, this study demonstrates that Vitoria’s international normative doctrines were a 16th century effort to promote universal ideas, which had some ethnocentric and pro-colonial distortions. This study considers the importance of the philosophical, theological and anthropological dimensions of Vitoria’s international legal doctrines. It analyses Vitoria’s views on the status of indigenous people, especially the Inca, in the 16th century historical context of the Spanish conquest of indigenous nations. Vitoria’s doctrine on the human nature of indigenous people was the foundation for his recognition of the existence of political communities in the New World, and the participation of indigenous nations in the international community. Vitoria’s rejection of medieval doctrines, on the universal authority of the pope, was the foundation for his dismissal of Spanish legal instruments, such as the Requerimiento, which justified the conquest of the Inca and other indigenous nations. Vitoria’s doctrines on the natural law of nations’ norms of trade, travel and evangelism were a central aspect of his normative justification for the Spanish presence in the New World. In the 16th century Spanish intellectual context, these norms were not inherently ethnocentric. However, because of Vitoria’s disregard of the consequences of the implementation of these norms in the historical context of the Spanish-indigenous nations’ international relations, they could have served to justify the Spanish conquest and colonization of the New World. This study shows that Vitoria’s most compelling justification for the Spanish use of force was the ending of the indigenous custom of human sacrifice, which was a violation of the right to life in the internal jurisdictions of indigenous nations.