School of Salamanca
The School of Salamanca, which gathered theologians such as Francisco de Vitoria (1480–1546) or Francisco Suárez (1548–1617), argued in favor of the existence of natural law, which thus gave some rights to indigenous people. However, while the School of Salamanca limited Charles V's imperial powers over colonized people, they also legitimized the conquest, defining the conditions of "Just War". For example, these theologians admitted the existence of the right for indigenous people to reject religious conversion, which was a novelty for Western philosophical thought. However, Suárez also conceived many particular cases — a casuistry — in which conquest was legitimized. Hence, war was justified if the indigenous people refused free transit and commerce to the Europeans; if they forced converts to return to idolatry; if there come to be a sufficient number of Christians in the newly discovered land that they wish to receive from the Pope a Christian government; if the indigenous people lacked just laws, magistrates, agricultural techniques, etc. In any case, title taken according to this principle must be exercised with Christian charity, warned Suárez, and for the advantage of the Indians. Henceforth, the School of Salamanca legitimized the conquest while at the same time limiting the absolute power of the sovereign, which was celebrated in others parts of Europe under the notion of the divine right of kings.