I've been keenly interested in this issue for quite some time.  At first, it looked like the Islamic Courts Union were going to pull off something almost unprecedented in the modern era, an act of state formation.  They had put together sufficient popular legitimacy and military force to drive out the warlords, and to start acting like a competent government.  Heck, they even took care of the pirates that were capturing cargo liners and holding their crews for ransoms.

Unwilling to sanction an "unauthorized" act of state formation, the US had to stop it.  After all, we can't let the "Islamofascists" win.  Nor could we have an actual, legitimate government emerge in Africa, one not controlled by Western interests or post-colonial elites.  We had a good ally in Ethiopia, who was for fairly basic strategic reasons not too keen on the re-emergence of Somalia as a functioning society.

It seems like it's only a matter of time before Ethiopia will have to pull back - if we can't afford the Iraq war, they certainly can't afford a Somali war.    With any luck, the Somalis will be able to pick up the pieces afterwards, and hopefully we will let them.