Before mass media you had media delivered via Mass through the Catholic church, which was substantially the same in not just the entire country, but in all countries.

Getting out of this was a century of real and cultural warfare that ultimately resulted in some of the first rights of countries, because forcing the centralization at the point of a gun was just not worth it.

Mass media is a much more recent, much more short term and much less powerful (there never was a newspaper czar and Walter Duranty could at most destroy your career, not burn you at the stake for telling the truth).

My point is that humans have had different groups with different values living inside the same countries for a long time before they considered themselves to be members of that nation, this is going back to what was normal, not reverting to something that is new.

Of course living with these separate groups wasn't exactly peaceful or without discrimination.