This is the Ukraine/Donbas problem in a teapot.

The cause is either different with I/P overtones or very similar but originating in centuries-old migration. Rather depends on who you talk to and where you talk to and whose perspective you adopt.

It would be nice to rely on facts, but "facts" are a bit malleable in this case--partly because the Ottomans sucked in many ways that it's uncomfortable to mention, partly because the Slavic governments since then sucked in pretty much the same ways. You can't trust the stats that form the basis of the "factual history." Either the Albanians were there straight along in their present numbers of there was migration or a demographic explosion.

It's a bit clearer in Macedonia.

And, of course, in both places we can't forget the little problem that the Serbs, at least the Tito-related factions, were strongly anti-Nazi Germany. The Albanian-speakers in Jugoslavija were sheltered and fought on the side of the Germans. The mufti of Jerusalem was of assistance in organizing this. It was one of those uncomfortable "progressive movements"--an alliance that we'd find unconscionable on the part of some and grounds for a principled rejection of their goals is utterly ignored when it suits us.