“The Church founded by the Redeemer is one, the same for all races and all nations. Beneath her dome, as beneath the vault of heaven, there is but one country for all nations and tongues; there is room for the development of every quality, advantage, task and vocation which God the Creator and Savior has allotted to individuals as well as to ethnical communities. [….] Whoever tampers with that unity and that indivisibility wrenches from the Spouse of Christ one of the diadems with which God Himself crowned her; he subjects a divine structure, which stands on eternal foundations, to criticism and transformation by architects whom the Father of Heaven never authorized to interfere.”
In other words, Jesus Christ came for all nations, and all nations are brought into one family within the Church. Therefore, (and here, Pius XI says it best):
“Whoever exalts race, or the people, or the State, or a particular form of State, or the depositories of power, or any other fundamental value of the human community – however necessary and honorable be their function in worldly things – whoever raises these notions above their standard value and divinizes them to an idolatrous level, distorts and perverts an order of the world planned and created by God; he is far from the true faith in God and from the concept of life which that faith upholds.”
So we can literally say that ideologies of racial supremacy (like Nazism) are a form of anti-Christianity idolatry. Just a reminder.
Oh, and in case this point was too subtly made, the pope issued this encyclical in German. (To my knowledge, it’s the only encyclical in history for which the official language was German.)