1) To void all those energy exploration and exploitation deals that Saddam and his ministers had signed with French, Russian, the Chinese, and other Governments, which excluded Anglo/Murkin 'interests,' and to forge new agreements which rectified those previous 'oversights.' Saddam and his guys weren't gonna renege on the previous deals, so they had to be "replaced" (i.e., 'killed'). The jewel in the crown is the new, proposed Iraq Oil Law, which grants huge favors and concessions to Anglo/Murkin concerns. Read all about it. It's passage will ratify the 'transformation' of Iraq into a 'working democracy' and guarantee the sitting Iraqi prime minister--mebbe, by then, Ahmad Chalabi will have popped up again--the title of "the Washington of the Tigris," or the "Lincoln of Mesopotamia" or some shit.
2) To launch a land-based air-craft carrier battle group into the heart of the resource-rich, hotly contested, tumultuous trans-Caspian energy pool. From bases in Kirkuk, for instance (which just happens to be the locale one of the four huge, 'temporary' bases nearly built now in Iraq), every population center--as well as every oil terminal, pipeline and depot--from the Bosporus to the Kyber Pass is within the effective, tactical range of supersonic, USer fighter-bombers. This is a vital necessity, if the USofA hopes to contain the energy ambitions of the Chinese, the Indians, and the re-emergent Russians. They didn't/don't call it the Grand Game for nothing.
3) To eliminate Iraq from the actors threatening Israel. Saddam Hussein probably signed his own death warrant when, during the 1st Gulf 'war,' he fired those ridiculous SCUD missiles into the Negev. His fate was sealed by the elevation to power in the US of the Chimp, a psychotic asshole "Sonny" who couldn't understand that Saddam's trying to off GHWB was just "bidness.' The denaturing of Iraq as a threat to Israel would be best accomplished by the Balkanization of the country, which could also be an outcome of the Iraq Oil Law, mentioned above.