Americanism was, in the years around 1900, a political and religious outlook attributed to some American Catholics and denounced as heresy by the Holy See.

In the 1890s, European "continental conservative" clerics detected signs of modernism or classical liberalism, which Pope Pius IX had condemned in the Syllabus of Errors in 1864, among the beliefs and teachings of many members of the American Catholic hierarchy, who denied the charges. Pope Leo XIII wrote against these ideas in a letter to Cardinal James Gibbons, published as Testem benevolentiae nostrae.

The long-term result was that the Irish Catholics who largely controlled the Catholic Church in the United States increasingly demonstrated total loyalty to the Pope, and suppressed traces of liberal thought in the Catholic colleges. At bottom, the conflict was cultural, as the continental conservative Europeans, angered at the heavy attacks on the Catholic Church in Germany, France and other countries, moved to stamp out the individualist attitude in America.