Pope Paul III, Sublimus Deus, 1537

…Christ, who is the Truth itself, that has never failed and can never fail, said to the preachers of the faith whom He chose for that office 'Go ye and teach all nations.' He said all, without exception, for all are capable of receiving the doctrines of the faith.
The enemy of the human race, who opposes all good deeds in order to bring men to destruction, beholding and envying this, invented a means never before heard of, by which he might hinder the preaching of God's word of Salvation to the people: he inspired his satellites who, to please him, have not hesitated to publish abroad that the Indians of the West and the South, and other people of whom We have recent knowledge should be treated as dumb brutes created for our service, pretending that they are incapable of receiving the Catholic Faith.

We, who, though unworthy, exercise on earth the power of our Lord and seek with all our might to bring those sheep of His flock who are outside into the fold committed to our charge, consider, however, that the Indians are truly men and that they are not only capable of understanding the Catholic Faith but, according to our information, they desire exceedingly to receive it. Desiring to provide ample remedy for these evils, We define and declare by these Our letters, or by any translation thereof signed by any notary public and sealed with the seal of any ecclesiastical dignitary, to which the same credit shall be given as to the originals, that, notwithstanding whatever may have been or may be said to the contrary, the said Indians and all other people who may later be discovered by Christians, are by no means to be deprived of their liberty or the possession of their property, even though they be outside the faith of Jesus Christ; and that they may and should, freely and legitimately, enjoy their liberty and the possession of their property; nor should they be in any way enslaved; should the contrary happen, it shall be null and have no effect.