The notion of a "civil war" in Iraq is a bit odd...
Since the US etal are the "occupying power" it is up to Washington to keep the peace in Iraq.
And any civil war the does develope would be odd indeed.
How exactly would the US military handle the situation...would the US take sides? Would the US military just stand back and let the fighting occur? The US military would be like the cops showing up at a "domestic dispute"...which all police will agree is their worst, and often most dangerous assignment!
Clearly to do whats required under international law...Dubya & Co may need to establish a draft just to avoid committing "war crimes" under international conventions about occupations and occupying powers.
The "Pottery Barn Rules" may YET need to be applied here...!