One difference from a caste system- foreigners are assigned the same racial categories as locals, whereas if I visited a society with a caste system, I simply w

One difference from a caste system- foreigners are assigned the same racial categories as locals, whereas if I visited a society with a caste system, I simply wouldn't have a caste, at least not by default. Black Africans in America are considered the same race as black Americans, regardless of sharing absolutely no recent ancestry whatsoever, and white Africans are the same race as white Americans, again without sharing any meaningful recent ancestry. A white Hispanic person will be treated as white (see: Ted Cruz) but a black one will be treated as black, even if they're literally siblings. Racial categories mean that a white American can feel more common ground with a white Russian than his black American neighbor. American white nationalist fellow-feeling toward Russian nationalists suggests to me that it's not really about suspicion of outsiders. Racial categories cut across borders, ancestry, language, and culture. Feeling confident that one can judge what category someone is in on sight without seeing their clothes, hearing them speak, learning their name, or knowing their ancestry is maybe not quite unique to modern racial ideas, but it certainly makes it stand out.