Not sure if this requires a pre-1900 POD, but as we know, concepts of race and ethnicity are rather unscientific and arbitrary. In the US Census today, we can see this (Chinese and Indian are both lumped together as "Asian," etc) and we can see the constantly-changing definitions of the past (Pacific Islanders were once grouped with Asians but aren't anymore, Mexican was once a race, etc). Other countries have different models - the Latin American division of different mixed-race groups, the Soviet and Chinese model of putting everyone into neat little ethnic boxes).
I'm curious to see what it would look like if different countries used different systems, for example, more countries using the Soviet system. France and Spain, for example, regarding themselves as multiethnic states with their various linguistic groups seen as ethnic minorities. China where "Han" is actually not one ethnic group but several, based on the unintelligibility of various Chinese dialects. The United States with an ethnicity-based system rather than a race-based one.
I'm curious to see what it would look like if different countries used different systems, for example, more countries using the Soviet system. France and Spain, for example, regarding themselves as multiethnic states with their various linguistic groups seen as ethnic minorities. China where "Han" is actually not one ethnic group but several, based on the unintelligibility of various Chinese dialects. The United States with an ethnicity-based system rather than a race-based one.