By the early 20th century, the descendants of the earlier Irish immigrants had successfully elevated Celts into the superior realm of northern Europeans.
Meanwhile, World War I dampened Americans’ ardor for “Saxon” — given its German associations — and increased the popularity of a new term liberated from Germanic associations. The new name was “Nordic.” Many German-Americans even altered their surnames during and after the war, but the notion of plural white races held on until World War II.
By the 1940s anthropologists announced that they had a new classification: white, Asian and black were the only real races. Each was unitary — no sub-races existed within each group. There was one Negroid race, one Mongoloid race, one Caucasoid race. Everyone considered white was the same as everyone else considered white. No Saxons. No Celts. No Southern Italians. No Eastern European Hebrews. This classification — however tattered — lives on, with mild alterations, even today.
The useful part of white identity’s vagueness is that whites don’t have to shoulder the burden of race in America, which, at the least, is utterly exhausting. A neutral racial identity is blandly uninteresting. In the 1970s, long after they had been accepted as “white,” Italians, Irish, Greeks, Jews and others proclaimed themselves “ethnic” Americans in order to forge a positive identity, at a time of “black is beautiful.” But this ethnic self-discovery did not alter the fact that whiteness continued to be defined, as before, primarily by what it isn’t: blackness.
Nell Irvin Painter, “What Is Whiteness?”, The New York Times (21 June 2015), SR8.