My point regarding various groups comes from observing Americans overseas.
If you asked your average 19 year old kid in Vietnam who he saw, the answer would likely be 'a bunch of gooks.'
Some of the more experienced people would say "those guys are Viet, but those are Annamese, while that group over there are Hmong, those guys are Korean and that group is ethnic Chinese. Some of them are Buddhist, while a lot of those are Roman Catholic, some are Animist, and others are hard core Communist."
Failure to understand who's who and what to expect of them often proved fatal.
Cultural differences amongst groups of identical ethnicity can be remarkable, and quite a few wars have resulted thereby.
FWIW the cultural differences where I work are basically occupational. It's more a matter of PhD vs MD, Biologists, Chemists, Electrical, Mechanical, or Chemical Engineers, Operators, HR, Accounting and Maintenance than of Country ABC or Ethnicity XYZ. If someone ever talks about 'back home,' it could turn out to be Alabama or Sierra Leone, Puerto Rico or Peru, but if they don't bring it up, it's immaterial.
The primary line of demarcation is either you are competent and reliable or you are not. That's it.
The key to getting past all the racist nonsense is to actively get over it. All the staring at your navel and wallowing in 'the conversation' does nothing but perpetuate the lines of division, which is unacceptable.
BSBD,
Winsor