Whilst I don't disagree that the US Divisions going to Yugoslavia doesn't appear to be a logical / sensible decision, I think it has been discussed on this forum before and a viewpoint was put forward that Civgov took the decision from a purely political point of view as a counter to Milgov, who at the time were sending reinforcements to Germany.
If I recall correctly, the proposed logic was that Civgov needed to show that it still had the capability to send troops to Europe as a way of scoring political points against Milgov as both are claiming to be the legitimate Government of the US and if one did send troops overseas and the other didn't, that would weaken the standing of the one that didn't.
That said, looking at this this morning, I'm not sure if there's an anomaly? I'm at work, so don't have access to any materials other than what I can source online, so am going off this timeline
http://www.d20.demon.nl/t2k/t2ktime.html
That states that the 76th and 80th Divisions are sent to Yugoslavia in October of 1998 (specifically late October inthe case of the 76th)
Same timeline then states that the split between US Governments took place on 19th April 1999, i.e. six months after those two Divisions were sent to Yugoslavia.
So if that's correct, it was only the 42nd Division that was specifically sent by Civgov - the other two Divisions were sent before the split, so presumably declared for Civgov at some point after 19th April 1999, at which point they were already in theatre. Or have I missed something (or is that timeline wrong)?
There are a whole host of things that if you study them in any sort of detail don't make sense, but they are what makes Twilight 2000 what it is. On this occasion I think it's simply a plot device to give those who might want to play a Balkans campaign with US player characters, in the same way that the RDF Sourcebook put Israeli units on the ground in Iran (which to me is about as plausible as Scotland winning the next World Cup) so that you could play Israeli PC's in an RDF campaign.