 The Spanish conquest of the Americas sparked a theological, political, and ethical debate about the use of military force to acquire control over foreign lands. This debate took place within the framework of a religious discourse that legitimized military conquest as a way to facilitate the conversion and salvation of indigenous peoples. The idea of a “civilizing mission” was by no means the invention of the British in the nineteenth century. The Spanish conquistadores and colonists explicitly justified their activities in the Americas in terms of a religious mission to bring Christianity to the native peoples. The Crusades provided the initial impetus for developing a legal doctrine that rationalized the conquest and possession of lands that were held by non-Christians. Whereas the Crusades were initially framed as defensive wars to reclaim Christian lands that had been conquered, the resulting theoretical innovations played an important role in subsequent attempts to justify the conquest of the Americas. The core claim was that the “Petrine mandate” to care for the souls of Christ’s human flock required Papal jurisdiction over temporal as well as spiritual matters, and this control extended to non-believers as well as believers.