Where to begin?
1.) Pope Urban IV, papal bull Cantate Domino:
The Church firmly believes, professes, and proclaims that those not living within the Catholic Church, not only pagans, but also Jews and heretics and schismatics cannot become participants in eternal life, but will depart “into everlasting fire which was prepared for the devil and his angels," unless before the end of life the same have been added to the flock; and that the** unity of the ecclesiastical body** is so strong that only to those remaining in it are the sacraments of the Church of benefit for salvation, and do fastings, almsgiving, and other functions of piety and exercises of Christian service produce eternal reward, and that no one, whatever almsgiving he has practiced, even if he has shed blood for the name of Christ, can be saved, unless he has remained in the bosom and unity of the Catholic Church.
2.) Pope Boniface VIII, papal bull Unam Sanctam:
We are compelled, our faith urging us, to believe and to hold; and we do firmly believe and simply confess; that there is one holy Catholic and Apostolic Church, outside of which there is no salvation or remission of sins; her Spouse proclaiming it in the canticles, “My dove, my undefiled is but one, she is the choice one of her that bore her;” which represents one mystical body, of which body the head is Christ, but of Christ, God. In this Church there is one Lord, one Faith, and one Baptism. There was one ark of Noah, indeed, at the time of the flood, symbolizing one Church; and this being finished in one cubit had, namely, one Noah as helmsman and commander. And, with the exception of this ark, all things existing upon the earth were, as we read, destroyed.
3.) Pope Pius XI, Mortalium Animos:
**In this one Church of Christ no man can be or remain who does not accept, recognize and obey the authority and supremacy of Peter and his legitimate successors. **Did not the ancestors of those who are now entangled in the errors of Photius and the Protestant reformers, obey the Bishop of Rome, the chief shepherd of souls? Alas their children left the home of their fathers, but it did not fall to the ground and perish for ever, for it was supported by God. Let them therefore return to their common Father, who, forgetting the insults previously heaped on the Apostolic See, will receive them in the most loving fashion. For if, as they continually state, they long to be united with Us and ours, why do they not hasten to enter the Church, “the Mother and mistress of all Christ’s faithful?” Let them hear Lactantius crying out: “The Catholic Church is alone in keeping the true worship. This is the fount of truth, this is the house of Faith, this is the temple of God: if any man enter not here, or if any man go forth from it, he is a stranger to the hope of life and salvation. Let none delude himself with obstinate wrangling. For life and salvation are here concerned, which will be lost and entirely destroyed, unless their interests are carefully and assiduously kept in mind.
So…
Pope Pius XI literally said that the Orthodox and Protestants will not have salvation unless they return to the visible Catholic Church.
If Pope Francis said that exact same thing today, in those exact same words, the world would accuse him of “bigotry” and “intolerance” towards other religions.