I can answer at least the Italian part.

The reason that Italians were looked down on in America is because of which part of Italy they came from. Italy is not a homogeneous country and in the south(especially in Sicily) there is Berber and Arab influences meaning the people are more olive skinned. Second Southern Italy is poorer than the north, a fact which is still causing problems today. So in the classification (read racist) crazy United States you have people arriving who don’t look white and don’t have the great American equalizer, money. It didn’t help that they were also willing to work for lower pay, so were taking jobs away from “White Americans”.

So they (A) don’t look like you, (B) are poor, and (C) are stealing your job. Queue Racism.