Here’s a portion of this encyclical:
"…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 people and that they are not only capable of understanding the Catholic Faith but, according to our information, they desire exceedingly to receive it…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.
By virtue of Our apostolic authority We define and declare by these present letters, or by any translation thereof signed by any notary public and sealed with the seal of any ecclesiastical dignitary, which shall thus command the same obedience as the originals, that the said Indians and other peoples should be converted to the faith of Jesus Christ by preaching the word of God and by the example of good and holy living…"
- Pope Paul III, Sublims Dei, 1537
This took place 500 years ago. The Catholic Church stood up for the rights of native peoples, defending their “personhood” and condemning the secular nation states for violating their rights and treating them like mere, “unensouled” animals.
It is my personal conviction that something similar will probably take place some time in the future. Mankind will discover alien life on other worlds, and then perhaps even intelligent alien life - other peoples. This will cause shock throughout the world similar to the shock caused by the discovery of the Native peoples of the Americas five hundred years ago.
The human race may colonate these other worlds, and some will probably subjugate the “alien natives” and deny that they are people.
Then the Catholic Church will be rocked by huge theological debate, with some theologians teaching that these “aliens” are not people with souls. However others will defend their personhood, and proclaim that to deny them the Gospel is like how some wanted to deny the Gospel to the native peoples of the Americas, which contravenes Christ’s command to evangelize all creation and thereby holds back his Second Coming.
Eventually, this party will win and a future Pope will probably issue a papal encyclical or apostolic constitution perhaps, that will proclaim that these alien peoples are “true people”, with immortal souls and that we humans do not have the right to treat them like mere animals.
And then we may find ourselves in a position where we have to preach the Gospel throughout the whole universe, so that Christ can return.