I understand what you mean. Very interesting. Well worth having, perhaps, a separate thread on the subject to further discuss.
The whole idea of homogeneous ethnic/linguistic “nationalities” grew up in the modern period in western Europe, where the facts on the ground bore some vague resemblance to the lines on the map.
It has been an utter disaster in eastern Europe and elsewhere in the world, where villages of different “nationalities” lived intermingled for many centuries, more or less in peace most of the time. When nationalism hit, the neighbors suddenly became interlopers in “my nation.”
There were parts of Macedonia in the late 19th and early 20th centuries that were claimed as their rightful property by Greece, Bulgaria, Turkey and Serbia all at the same time. The Albanians and/or Montenegrins might have been in on the act, too.
Claims ranged from historic to linguistic to racial. Maps were produced showing the “true boundaries” of the various “nations,” with massive overlapping.
Yet it’s perfectly obvious that it wasn’t possible for more than one of these claims to be implemented.
America has managed to dodge most of these bullets, as one can easily become and be accepted as an American. If you’re born a Bulgarian, you can’t become a Serb, at least not without betraying your entire heritage.
The Habsburg (Austr0-Hungarian) Empire lasted centuries under the rule of a more or less absolute autocrat. Aristocrats of all the “nationalities,” (German, Hungarian, Polish, Croat, Czech, etc.) all worked for the empire, more or less in equality. That being of course an equality between nobles. All of them together lording it over the peasants.
When nationalism became popular, this all fell apart. If the empire was to be German or Magyar, then the Slavs had no real place in it. Unless they wanted to stop being Slavs and become Germans or Hungarians. Assuming the Gs or Hs would let them do so.