> something changed

It's worth considering what changed. Demographics changed, but we've always had some kind of mixed cultures and ethnicities. The history of it has been an expansion of who gets to be the "majority". Like Rome redefining who is a citizen.

Maybe it's broadcast media, but there's been national publications since the founding of the US.

Looking back to Antiquity, our situation doesn't seem so abnormal. I think it's just the ebb and flow of how groups of people interact with each other.