This article confronts two philosophical positions that define the nature of international order in matters concerning state legitimacy and the justifications for the recourse to war. The first position, set forth by Francisco de Vitoria in the sixteenth century, frames legitimacy and the use of force within the traditional, Christian natural law conception of justice. Legitimate are those states that uphold universal principles of justice, not the political principles of a particular regime form, while the recourse to war is likewise justified by the constitutive tenets of the ius ad bellum and the ius in bello. By contrast, Rawls' Law of Peoples, which compares itself to the Christian natural law tradition, articulates nonetheless a particular liberal conception of justice that defines legitimacy in wholly political terms. In addition, in its appeal to the so-called 'supreme emergency exemption' the Rawlsian Law of Peoples dispenses with a crucial aspect of the traditional ius in bello that prohibits the targeting of civilian populations, as an exceptional means for defending and promoting a liberal international order. It is argued that such an ideologically based view of order posits a non-inclusive conception of justice in a culturally and politically diverse world and, hence, encourages conflict, resistance and strife between liberal and non-liberal states, and even strengthens autocratic government beyond the liberal zone of peace. A more tolerant and sound view, held by Terry Nardin's conception of 'common morality', is similar to Vitoria's traditional conception of a more politically tolerant justice-based order and expresses in contemporary ethical language the principal tenets of the tradition of the laws of war set forth by Vitoria himself.