One of the things that you learn as you study history is that at some point someone has tried to explain everything from positions that don’t hold water. As a young nation, which America still was in the early 1800s it was wildly xenophobic. Worse as a large part of the movers and shakers who built America were from England their reaction to the Irish either Protestant or Catholic wasn’t always pleasant. The Irish in turn lashed out. Despite getting to vote fresh off the boat, no bars on employment and often language barriers as even the Gaelic speakers were integrated into the police, fire, political and union machinery, they lashed out at blacks to bolster their position.
This link is a pdf that I tripped over the other day that takes a look at things: click here