In America, we've been doing it to ourselves for decades. I would trace it to at least the mid-90s, following patterns set up in the 50s and 60s. It's the same thing we've always done, magnified first by mass media, then by social media.

I don't know why it seems to work so well in other places. Europe, presumably, has even older divisions to employ. They're hardly immune to the basic foibles of Americans.