"Irish immigration essentially spurred our Civil War"
Nit, I think it mostly contributed city folk who couldn't shoot well cannon fodder (the NRA was explicitly established because of poor Union marksmanship). But quantity has its own quality, and Grant won in part because he realized that.
They weren't part of the New English Moralists who played one of the biggest roles in triggering it, nor I'm pretty sure were harmed like Lincoln's family by competition from slaves, and how much political power did they have back then?