that it ought to be resorted to only when it was necessary to prevent an even greater evil. A diplomatic agreement is preferable, even for the more powerful party, before a war is started. Examples of "just war" are: In self-defense, as long as there is a reasonable possibility of success. If failure is a foregone conclusion, then it is just a wasteful spilling of blood. Preventive war against a tyrant who is about to attack. War to punish a guilty enemy. A war is not legitimate or illegitimate simply based on its original motivation: it must comply with a series of additional requirements: It is necessary that the response be commensurate with the evil; use of more violence than is strictly necessary would constitute an unjust war. Governing authorities declare war, but their decision is not sufficient cause to begin a war. If the people oppose a war, then it is illegitimate. The people have a right to depose a government that is waging, or is about to wage, an unjust war. Once war has begun, there remain moral limits to action. For example, one may not attack innocents or kill hostages. War is only legitimate as a last resort, after vigorous attempts at negotiation and diplomacy have failed. Under this doctrine, expansionist wars, wars of pillage, wars to convert infidels or pagans, and wars for glory are all inherently unjust. The conquest of America In the 16th century, the School of Salamanca was the first to use the natural law's principle that rights reside in the individual to question the Spanish colonization on the indigenous people of the Americas. Francisco de Vitoria began his analysis of conquest by rejecting "illegitimate titles". He was the first to dare to question whether the bulls of Alexander VI known collectively as the Bulls of Donation were a valid title of dominion over the newly discovered territories. In this matter he did not accept the universal primacy of the emperor, the authority of the pope (because the pope, according to him, lacked temporal power), nor the claim of voluntary submission or conversion of the Native Americans. One could not dismiss them as sinners or ignorant savages: they were free people by nature, with legitimate property rights. When the Spanish arrived in America they brought no legitimate title to occupy and rule those lands. Vitoria also analyzed whether there were legitimate claims of