yes, there were so many differnet reasons, the reason at the front kept changing as well. "bringing democarcy to the middle east" was only really pushed as a stated aim after the whole WMD reason fell apart. but i guess you could just say it was a mix of
energy security and control, reassert US dominance in the region and beyond and establish a new garrison state with a compliant puppet government in the middle east as Saudi arabia was kicking US troops out.
Fot the neo cons who love this whole spreading democracy BS it was a dream come true. palestine had free elections, they voted in Hamas, Algeria had free elections and they voted in the islamic FIS, if egypt wasnt a brutal one party state and held real elections then the muslim brotherhood would probably win there. turkey had them and the islamic welfare party won there. spreading democracy via free elections doesnt win the US any friends in the middle east, spreading democracy via an invasion and keeping 150,000 troops does.
you could also take a step back and see the logic of a miltary industrial complex the US has built up needs a enemy, it needed one weak enough so it could be easily crushed(north korea was out then, as is china,russia) but strong enough so it could demonise it for public consumption ( a small island in the carribean sea wont do this time, or a small central american nation. just too 1980s, islam is the new thing) and finally it needs to contain resources (sorry rwanda,somalia you just wont do) to pay for the operation. the neo cons 5 years ago were claiming that within a year iraq could pay back the cost of the operation and the whole thing would turn a profit.
complete folly and such a waste