Eastern Europe is a brewing pot of cultural diversity and history.
Macedonians regularly apply for Bulgarian citizenship if they can prove their origin is from Bulgaria, so as to get a backdoor into the EU, they get a Bulgarian passport. [1]
Eastern Europe / the Balkans are pretty complex. They have been ruled by The first and second Bulgarian Empires, The Byzantine Empire, the Roman Empire, and the Ottomans.
[1] https://www.novinite.com/articles/112811/Bulgarian+Passports....
Pretty much sums it up, but you forgot the Most Serene Republic of Venice :)
Also, it might be worth noting that although influenced by the Soviet Union, Yugoslavia and Albania separately broke ties with Stalin in a pretty bold move for the time.
1) It was already on the periphery of the SU sphere of influence, not central (unlike the unlucky Hungary, Czechoslovakia etc)
2) It was already agreed it will be 50:50 sphere of influence SU:US, at Yalta conference only couple of years back
3) In 1948 SU still lacked the atom bomb, while US already got it
4) Memory of WW2 still very fresh, would SU risk confrontation with US over far&away lands
[1] https://www.dw.com/en/bulgarian-passport-scam-officials-arre...
Funnily, the equivalent running joke in Serbia is that Macedonians are Serbs with a speech disorder.
Having left the Balkans, I find it very liberating, these days, when a proposal or idea of mine gets shot down, that I don't have to wonder: "Did they think I am a liar?", "Did I not articulate it over well enough?" and the like. It is such a relief, to know - it was most likely the idea, not myself.
Which is the kind of disputes big nations use to influence local policies, sell weapons, create satellite states, etc, to use for their higher-stakes disputes...
Meanwhile, the big western nations that started 2 world wars, gassed 6 million people (plus some tens of thousands of soldiers in WWI), and gone to war and occupied peoples all around the globe as colonial powers, somehow managed to even pin WWI on the Balkans (as if it was the assassination of Archduke Franz Ferdinand the cause, and not a mere pretext, the cause being western european power plays, of the same powers that were the dominant forces in the war).
There's a current dispute between Bulgaria and (North) Macedonia. Basically, Bulgaria is not willing to recognize the Macedonian language, with their vice-prime-minister recently saying it's the "Esperanto language on the Balkans". They're also veto Macedonia's EU membership negotiations. It's an ongoing, heated discussion which has (unfortunately) caused hatred between the countries (North Macedonia and Bulgaria have been mostly friendly between each other in the past).