Salt is good (I'm almost done with it). To go along with the North-is-virtuous debunking, I'd recommend Noel Ignatiev's How The Irish Became White. It's quite an eye-opener and really demonstrates that the Irish, far from being persecuted victims in the US, victimized African Americans pretty thoroughly right from the start. (I am speaking as someone of Irish descent who heard all of the "poor me" stories from me dear old granny about the persecution of the Irish by the Brits, first, and then the WASPs in the US.)
They had lots o' Negroes over there in County Cork, did they? The Irish may have been kicking blacks good in America in the 19th century, but that doesn't absolve 600 years of English exploitation and religious persecution, not to mention the forced displacement of property owners and the rent system, which was on par to the Russian serfdom.
Erin go bragh!