I don’t know what you’re saying? Are you saying that the US treated South American[s?] poorly in the past therefore they are experiencing brain drain[1] which i

I don’t know what you’re saying? Are you saying that the US treated South American[s?] poorly in the past therefore they are experiencing brain drain[1] which is significant compared to the brain drain Russia is experiencing? I think that’s patently false but I can’t work out how else to parse your sentence. [1] Note that, on net, the US is experiencing ‘brain accumulation’ (especially in science/tech) not brain drain, despite the slightly broken immigration system.