Early in 1532, the Catholic professor Fransisco de Vitoria lectured his students ‘On the Power of the Church’ at the University of Salamanca. Efforts like this to defend the status of the Church led, perhaps paradoxically, to a new appreciation of the state’s foundations and its basis in the order of nature. Vitoria was anxious to protect the authority of the universal Church, he also believed that there should exist a multiplicity of civil powers, each with its own integrity and degree of autonomy. While there could only be one true Church, there could and should be many commonwealths; he, like many others, was sceptical of imperial ambitions in the temporal sphere. His thinking, and that of other Catholics like Bartolomé de Las Casas, generated a critique of political or temporal empire that would gather momentum as reports of Spanish cruelty in the New World began to circulate. Yet there were also Catholics, like Juan Ginés de Sepúlveda, who embraced the pursuit of empire and sought to defend it, often using classical ideas but adapting them to current circumstances. As this clash of beliefs unfolded, it came to include lengthy reflection on power, natural rights and authority, including the influential work of Fernando Vázquez de Menchaca. At the heart of the debate was a question about the relationship between a universal natural law and the particular rules and commands of specific communities, be they the Catholic Church or localized political communities.