One of the main confounds seems to be "large immigrant group". For example, even ethnically-100%-Spanish Latinos in the U.S. are considered different from "Angl

One of the main confounds seems to be "large immigrant group". For example, even ethnically-100%-Spanish Latinos in the U.S. are considered different from "Anglos", in significant part because it's a large group. That sometimes leads to significant differences between countries. I'd say that for the past 50 years or so, Greek-Americans have been considered part of the undifferentiated majority "white" population. But Greek-Australians are still considered different in Australia, not really properly white, or at least white with an "ethnic" asterisk.