The History of White People, by Nell Irvin Painter

I am in the middle of this very interesting book. You might expect that the book would have a lot to say about the history of dividing black from white. But there is much more about American theorizing about the differences between the various "European" races, and about which were superior or inferior. I was not completely unaware of the disapprobation of "native" (white) Americans for poor, Catholic Irish immigrants (among them some of my ancestors), but I was taken aback by the amount of energy during the 19th century into proving that the "Celtic" race was at the bottom of the stack, and a menace.

And there's this note on page 107:

Rhode Island delayed ratification of the Fifteenth Amendment to the Constitution until 1870, because legislators feared that it might enfranchise members of the Celtic race. Black men had been able to vote there since 1840.