Sowing the Seeds of Ethnic Clashes: Hungarian Stormtroopers???

From the last two posts on the Balkans, you can see that the region is terrifically diverse, both ethnically and religiously. Now that the ethnic and religious divides have been loosely spelled out, the next step is to try and highlight some of the specific historical events that sowed the seeds of division and all-out rancor.
WWII
In the early part of WWII, the Balkans were relatively unaffected, and, until 1941, the only violence the region experienced was a war fought along the Greek/Italy border. However, before Hitler dispatched his troops on their grand, ill-fated march up to Russia, he ordered the securing of the Balkans. This was not a tall order, given the decentralized nature of the region and its corresponding lack of military might; the campaign ended around the same time it started, with a few more feathers in the now-overcrowded Nazi cap.

This left the Balkan states with essentially one of three fates:
(1) Get directly in bed with Germany/Sell soul, etc.
(2) Squirm, but ultimately surrender, as the puppetmaster pulls the strings on your sham gov't
(3) Run for the hills and serve out ineffectual existence in exile
(a): spearhead guerrilla insurrection all but destined for immediate and total suppression by Nazis

Bowing to the Nazis
Bad options all, but the more, shall we say, pragmatic favored the short-term bliss of surrendering to their Nazi bride...and lived to regret it. This group included Bulgaria, Hungary and Romania.
Perks: regaining lands lost in Treaty of Versailles through partitioning of Czechoslovakia (Hungary); strength of Nazi state at your back (all)
Downsides: being forced to dispatch troops for German-led campaigns in the horrific wars on the Eastern front with the creatively brutal and macabre Russian troops (Hungary); losing lands/being used as a pawn between Russia and Germany (Romania); lasting stigma/fallout of alliance with Nazis (all)

Yugoslavia
Initially, Yugoslavia's leader signed an alliance deal with the Nazis, but was overthrown by lusty freedom-fighting Serbs. However, the Germans did not countenance this for long: Yugoslavia was soon invaded and partitioned. Croatia, including Bosnia, was placed under puppet rule; Serbia was under German military rule; Macedonia was given to Bulgaria.
Germany's policies were specifically aimed at denigrating Serbs and, when there were rumblings of armed insurgency, the Germans suppressed them swiftly and brutally.

Life in Exile...
Greece: Greek Royals fled to Egypt, and the remaining Greeks were all across the board in terms of allegiances and alliances. Some communist guerrillas engaged in armed resistance; others were actively involved with British Commandos. There were also some factions who did not recognize the Royal gov't anyway.

Nazi Puppet Strings
Croatia: the Germans set up a government ruled by the Utashe based on anti-Serb/anti-Orthodox sentiments. The Utashe went into Serb villages and forced residents to convert to Catholicism and many enemies of the puppet state were sent to death camps. The Bosnian Muslims were left alone, inexplicably. This is where we start to see the fires stoked even more. Like colonial regimes in Rwanda and Indonesia , ethnic and cultural distinctions were exploited for the overlords' gain (between Hutus and Tutsis and Chinese and Indonesian, respectively), aggravating fault lines that would later be prodded by poorly drawn boundaries or the mere side-by-side existence of these ethnic enemies.