Italians and Irish discriminated against each other as they immigrated to the US since, as noted above, they were at the bottom of the barrel and discriminated against by the other Western European immigrants (Germans, English, etc).

St Louis is a very good example of the dynamic. Kerry Patch was the Irish section on the north side and the Hill was the Italian section on the south side. The Irish came first and they held political office and controlled the police department. Of course, the Irish has OC.

The Italians arrived and by the 50's, had largely wiped out the Irish OC elements and taken over the rackets. They also entered politics.

My Irish grandfather discriminated against anyone who was not Irish - he was an equal opportunity hater. I believe it was a way of life back then, and due to ignorance. Suburbia brought the different ethnicities together, and played a role in reducing the discrimination and assimilation.

Today, Kerry Patch is a ghetto as all the Irish left to the suburds. The Hill is a very nice neighborhood and largely Italian.

BTW - my grandfather's racism was not limited to Europeans. When my uncle came home from WWII and had nightmares and trauma from his experiences as a marine fighting the Japanese in the Pacific, my grandfather developed a hatred for anyone Asian, and referred to them all as "dirty japs". Did not matter if they were Chinese or Korean, they were all hated. Ignorance at its very finest.