What exactly is this? Edited to add, I know the term dates back to Pope Leo, but that was over 100 years ago. Where do you see it now? It’s an antiquated term.
There is a book that I read from Ignatius Press that discuss the Americanism heresy. According to the book, the Americanism heresy had its largest impact during the early to mid 20th Century, in the decades before the Second Vatican Council.
The Americanism Heresy finalized in the idea that Catholic ghettos and Catholic only adult sports leagues/clubs (like the Catholic Bowling Leagues in Philadelphia) needed to be closed. The Americanism Heresy also lead to the ideas that moved the Land o Lakes Conference forward, etc.
In other words, the “fruits” of the Americanism Heresy was the concept that in order for Catholicism to be accepted in America, Catholics had to be no different from other Christians. The Americanism Heresy is what lead to many Catholics abandoning the Rosary and other Sacramentals in many areas of the country, esp the areas that were not heavily Catholic.
The vast number of American Catholics I know from both Americas use at least some sacramentals.
The “America” that the Americanism heresy deals with is the United States. South America wasn’t really affected by it, at least not directly. Same with Canada.
And the vast majority of American Catholics I grew up with in Delaware (which Methodism was the largest denomination when I was a child) never made use of sacramentals unless they were born before World War II. I never knew any Baby Boomers (or Gen X) who made consistent use of sacramentals.
It wasn’t until I moved from the Diocese of Wilmington to the Archdiocese of Philadelphia that I began to see Catholics who actually used Rosaries or talked with pride about their Catholic childhood & family traditions.