Historian here, I would agree that it’s not going to be as simple as looking at ethnicity. You also need to look at region and particularly at economic competition. For example, there were Irish immigrants and free Blacks in antebellum New York City who shared neighborhoods, saloons, and intermixed culture (where tap dancing comes from), but you can also find wealthy Blacks hiring the Irish as servants in Boston and looking down on them, and you can also find virulent, ugly racism in Irish-American communities made visible in the Boston Busing Crisis, for instance.