Yet racism and anti-racism seem to have many of the same political phenomena and silliness in say Brazil as they do in the US.

I'm not so sure about that - in Europe there's been a good deal of friction between groups that are not that different; even when there's a "smooth continuum" of people (in terms of physical appearance and genetics), language and religion can constitute discrete enough differences to cause friction similar to racism in the US (see Belgium, or Ireland, or Yugoslavia, or the Basques ...). Of course, added to that there are some recent immigrants that are so different from the "natives" that it makes more sense to speak of "racism".

I think the cultural importance of the US combined with it's pretty special demography (people from "very" different backgrounds, not that mixed until recently) makes black-white racism the archetypical "friction and animosity between groups", whereas historically, it's a bit of an outlier.