100 years ago, the KKK planted bombs at a U.S. university – part of the terror group's crusade against American Catholics

To be 100% American, in the Klan's view, meant that you were a white Protestant Christian. 

In the years between 1890 and 1920, a flood of immigrants from southern and eastern Europe came to America, a large percentage of whom were Catholic or Jewish. 

While the Klan was – and still is – strongly antisemitic, in the 1920s its members were particularly worried about Catholics, as there were many more of them. This was certainly the case in Dayton, where 35% of churchgoers were Catholic, thanks to an influx of immigrants who worked in the city's factories...

https://theconversation.com/100-years-ago-the-kkk-planted-bombs-at-a-u-s-university-part-of-the-terror-groups-crusade-against-american-catholics-219287