You know Vaudeville? The one where the white men paint themselves black and dress in white and red suits, with the hats. Strumming on the banjo, harmonica, all that old south stuff.
That was begun by the Irish because they shared more in common with the free blacks than with the New York people.
Another mark against the Irish was because they were Papist. As far out as it sounds that John Paul II could command so many people, alot of 1890s Americans were afraid of Catholics and despised them.