Through its investigation, this book highlights how Salamancans and related thinkers clearly distinguished their understandings of political order from medieval thought, and did so in a different way to contemporary and later thinkers, such as Machiavelli, Luther, Bodin, and Grotius, particularly with regards to the Indies, “barbarian” worlds. It also reveals the strong contribution of the School of Salamanca in early modern political thought, both internally and externally. Salamancans imposed moral restrictions against “interior barbarism,” that is, power beyond law, and included “exterior barbarism,” that is, “barbarian” societies, in the common political order. Situating the School of Salamanca in the mainstream history of European political thought, is ideal for academics and postgraduate students of intellectual history and of Spanish colonial expansion.