The millions figure is gross hyperbole. There were about 6K or so Croats and Muslims in SS "divisions." They were very ineffectual for the Nazis. Tito slaughtered many more Serbs actually than the ethnic SS "divisions" did, those who supported the king, and actually slaughtered many more Croats and Muslims that the SS divisions did. In any event, fighting old wars, rather than dealing with the present is a dead end. I hope Serbia is absorbing that. I think they are, I hope they are, but I am not sure. Most of Europe has got out of the business of worrying about borders. One hopes the Balkans follow suit.
Tito was a Croatian.
I sense a bit of sarcasm here. If not, keep in mind that only about 4% of Europeans consider themselves "European" first. The rest think of themselves as "French," "German," "Irish," "Italian," etc. European nations do still survive, in spite of their governments attempts to destroy the nation-state. And that is precisely why the envisioned "United States of Europe" will never come to pass. The EU will die. It is not a matter of "if," but "when."
On the Balkans specifically, it would help to remember that the whole Land of the South Slavs ("Yugoslavia") WAS united under one banner, and it ended up splitting up. That is exactly what will happen if Europe tries to melt itself together completely.