Francisco de Vitoria and the Evolution of International Law: Justifying Injustice is a reconstruction of the philosophical and legal theories of Fray Francisco de Vitoria, hailed by many as one of the primary founders of international law, and how these served to introduce the theory of an international community in which all nations take part, regardless of religious beliefs. The impact of the conquest of the Americas resulted in a transformation or re-articulation of the Old World’s preconceived notions of human nature and the rights of people and nations. Due to the need for a more universal principle, the theory of international law began to expand. In order to present a perspective on international law and human rights beyond the scope of the Spanish conquest of the Americas, Vitoria’s thoughts are compared to those of Hugo Grotius and John Locke, to show how the issues of natural, human, and divine law evolved through time. Their questioning of the right to invade other countries and subdue their inhabitants brought to light the conflictive relationship between colonial expansion and the law of nations and was an essential part of debates among intellectuals, jurists, and theologians in an attempt to find a way to reconcile these two often-contradictory notions.