A question that dawned on me as I revised my post-Valkyrie Cold War maps and proto-TL notes:
A plan that circled in the Comintern and the Soviet bloc up to the early phases of the Cold War was to build the Balkan Federation, some kind of confederal setup between Communist Yugoslavia, Bulgaria, Albania, Greece, and Romania. IOTL the Tito-Stalin split put an end to such plans.
Now let's assume that for whatever reason, Tito is not in the position to defy Stalin and Yugoslavia remains true to Soviet allegiance, so those plans are implemented.
I'm going to use the Valkyrie successful PoD, which sets the Iron Curtain rather eastward and makes Stalin go nastier on his slice of Europe: post-Nazi Germany bargains national unity in the post-Anschluss borders and no Soviet occupation for its surrender, Czechia, Slovenia, and Croatia remain in the Western camp, the Iron Curtain is set on the Vistula and the Danube, matching front lines in late 1944 and splitting Poland and Hungary in two. Stalin is pushed into enforcing rushed hard-core Sovietization of everything the Red Army has boots in, including Finland and Yugoslavia. As a result, the Balkan Federation is established betwen loyal Stalinist rump Yugoslavia, Bulgaria, Albania, and Romania (Greece remains in the Western camp as IOTL). But of course, several other PoDs that nullify the Titoist split are possible.
Now, when the Soviet bloc collapses (most likely 5-15 years earlier or so if we use my PoD, as it would be rather smaller and poorer), the Balkan Federation would surely collapse as well with it as an hated Communist artifact. All the same, its previous existence would blur the border lines in the Balkans somewhat, and give successor nations with rival nationalistic claims added fuel and legitimation for them.
Let's say that Bulgaria is thus able and motivated to renew its old claims on FYROM, and the latter's Bulgar character was not so stamped out as IOTL. Similarly, Albania has an enhanced claim to Kosovo. When rump Yugoslavia collapses, Bulgaria and Albania join the Yugoslav successor wars against Serbia. Quite possibly, Greece supports Bulgaria as an attempt to prevent the distasteful existence of independent FYROM. All the same, Serbia also attempts to clamp down harder on Bosnia, since it does not have any realistic chance of making a bid on Croatian Krajina. OTOH, NATO and EU most likely keep long-standing member Croatia into line, so it does not jump on Bosnia as well.
How would these different post-Yugoslav wars turn out ??