Why Pope Leo XIII in 1899 had to warn against "Americanism" as a threat to Catholicism

TESTEM BENEVOLENTIAE NOSTRAE Concerning New Opinions, Virtue, Nature And Grace, With Regard To Americanism

Pope Leo XIII

Encyclical promulgated on January 22, 1899.To Our Beloved Son, James Cardinal Gibbons, Cardinal Priest of the Title Sancta Maria, Beyond the Tiber, Archbishop of Baltimore: Beloved Son, Health and Apostolic Blessing: We send to you by this letter a renewed expression of that good will which we have not failed during the course of our pontificate to manifest frequently to you and to your colleagues in the episcopate and to the whole American people, availing ourselves of every opportunity offered us by the progress of your church or whatever you have done for safeguarding and promoting Catholic interests. Moreover, we have often considered and admired the noble gifts of your nation which enable the American people to be alive to every good work which promotes the good of humanity and the splendor of civilization. Although this letter is not intended, as preceding ones, to repeat the words of praise so often spoken, but rather to call attention to some things to be avoided and corrected; still because it is conceived in that same spirit of apostolic charity which has inspired all our letters, we shall expect that you will take it as another proof of our love; the more so because it is intended to suppress certain contentions which have arisen lately among you to the detriment of the peace of many souls. It is known to you, beloved son, that the biography of Isaac Thomas Hecker, especially through the action of those who under took to translate or interpret it in a foreign language, has excited not a little controversy, on account of certain opinions brought forward concerning the way of leading Christian life. We, therefore, on account of our apostolic office, having to guard the integrity of the faith and the security of the faithful, are desirous of writing to you more at length concerning this whole matter. The underlying principle of these new opinions is that, in order to more easily attract those who differ from her, the Church should shape her teachings more in accord with the spirit of the age and relax some of her ancient severity and make some concessions to new opinions. Many think that these concessions should be made not only in regard to ways of living, but even in regard to doctrines which belong to the deposit of the faith. They contend that it would be opportune, in order to gain those who differ from us, to omit certain points of her teaching which are of lesser importance, and to tone down the meaning which the Church has always attached to them. It does not need many words, beloved son, to prove the falsity of these ideas if the nature and origin of the doctrine which the Church proposes are recalled to mind. The Vatican Council says concerning this point: "For the doctrine of faith which God has revealed has not been proposed, like a philosophical invention to be perfected by human ingenuity, but has been delivered as a divine deposit to the Spouse of Christ to be faithfully kept and infallibly declared. Hence that meaning of the sacred dogmas is perpetually to be retained which our Holy Mother, the Church, has once declared, nor is that meaning ever to be departed from under the pretense or pretext of a deeper comprehension of them." —Constitutio de Fide Catholica, Chapter iv Read it all:  https://www.ewtn.com/library/PAPALDOC/L13TESTE.HTM