It was kind of internecine warfare among Irish immigrants.
They were all looked down upon by the Brahmins and pretty much everone else, so displays of economic success were important to the "Lace Curtain" Irish.
I grew up in a mill city were there actually where "Irish Need Not Apply" signs were posted.
An accent one rarely hears these days is the “Locust Valley Lockjaw” of the old Anglo and Dutch families in the New York area. Think FDR, William F. Buckley, and Thurston Howell.
My Grandfather’s people were from Northern Ireland, County Armagh, I think.
“”Shanty Irish” were looked down upon by earlier Irish immigrants who had achieved a measure of economic success...”
That is the origin of the term “scots-irish” or “scotch-irish” as some say.
Before the arrival of the famine settlers (shanty irish)from Ireland in the 1840s, the earlier immigrants and their descendants called themselves “Irish.”
But the famine folks were a motley bunch, hence a new term had to go into use to name the older, established respectable ones: “scots-irish.”
The first big significant immigration of “scots-irish” was five ships, in 1718 landing at Boston. From there they spread out.
Later and bigger immigrations settled Pennsylvania and mainly southward after migrating and so forth.
I come from a line of the 1718 bunch, who moved a few times.