Juan Ginés de Sepúlveda On the Reasons for the Just War among the Indians (1547),

So how did the Spanish justify their New World conquests? One of their most prominent ideologues was Sepúlveda. See the link for more of his justifications for Spanish imperialism.

Now compare these natural qualities of judgment, talent, magnanimity, temperance, humanity, and religion with those of these pitiful men [the Indians], in whom you will scarcely find any vestiges of humanness. These people possess neither science nor even an alphabet, nor do they preserve any monuments of their history except for some obscure and vague reminiscences depicted in certain paintings, nor do they have written laws, but barbarous institutions and customs. In regard to their virtues, how much restraint or gentleness are you to expect of men who are devoted to all kinds of intemperate acts and abominable lewdness, including the eating of human flesh? And you must realize that prior to the arrival of the Christians, they did not live in that peaceful kingdom of Saturn that the poets imagine, but on the contrary they made war against one another continually and fiercely, with such fury that victory was of no meaning if they did not satiate their monstrous hunger with the flesh of their enemies…. These Indians are so cowardly and timid that they could scarcely resist the mere presence of our soldiers. Many times thousands upon thousands of them scattered, fleeing like women before a very few Spaniards, who amounted to fewer than a hundred….

How are we to doubt that these people, so uncultivated, so barbarous, and so contaminated with such impiety and lewdness, have not been justly conquered by so excellent, pious, and supremely just a king as Ferdinand the Catholic was and the Emperor Charles now is, the kings of a most humane and excellent nation rich in all varieties of virtue?

Source: http://www.chss.montclair.edu/~landwebj/105/1sepulve.htm