Fur Shur more blacks were lynched by the KKK than Catholics by Protestants in America ~ by a factor of 100,000 I am sure!
The Know Nothings were a political party. The KKK sought to deprive blacks of all civil rights ~ and they enforced their ambitions with murder.
Now, let's turn our attention to Mexico ~ as I recall Sam Huston and other American Protestants were FORCED by Mexico to become Catholics in order to be allowed to settle Tejas!
This was way back there in the 1830/40 period.
Now there's a REAL "Know Nothing"/"Catholic" situation ~ but you will find, if you dig deep enough, that the Protestant dominated United States of America backed the Roman Catholic Republic of Texas to the hilt in their efforts to free themselves from the corrupt rule of Santa Anna!
This stuff was current news in those days and it could not help but fire the flames of bigotry and prejudice of the time.
I'd suggest you take up the greater part of the argument set forth by this author with the MEXICAN government ~ ask them for reparations for the FORCED CONVERSIONS!!!!
Of course it did, because the US as a nation has always been the safeguard of the poor and beleagured.
The KKK and the Know-Nothings were/are not representative of the US as a nation in any way.