I just wanted to add some further support to your argument, Constance. Although countries like China are hugely diverse, it’s still a single country. Mexico too. Those racialised as Black are not only from a huge diversity of different national backgrounds, they are also one of the most diverse “racial groups” on the planet. Here’s an intetesting article if you wanted a citation:

https://amp-theguardian-com.cdn.ampproject.org/c/s/amp.theguardian.com/world/2020/jan/26/fight-racism-using-science-race-genetics-bigotry-african-americans-sport-linnaeus