A leaked State Department memo details the plans for post-war rebuilding of Iraq. One line in the memo specifically mentions military occupation and describes the planned timeline as years, not months. The real question is: Who is going to supply the troops?
The Pentagon has based its force structure on a murky and muddled concept called 2MRC for Two Major Regional Conflicts. The intention was to build the force to be able to fight a war simultaneously in Iraq and Korea. One major reason this strategy was developed was because Congress capped the end strength of the Army at 495,000 and the other services equally low, with regards to the missions assigned them.
Assuming the US conquers Iraq and has to occupy it, where do the forces come from? They cant reduce the commitment to the Korean peninsula after all, that is part of the 2MRC strategy. But forces earmarked for that conflict, and for any Middle East conflict are already deployed. There are peacekeeping missions in Bosnia, Macedonia, and Kosovo, counter-terrorist operations in Afghanistan, Pakistan, the Philippines, and now, Yemen. Troops are deployed supporting these missions in Hungary, Greece, Italy, Uzbekistan, Turkey, Singapore, Djibouti, and (not officially) Georgia, Azerbaijan, Thailand, Indonesia, and Khazakstan.
Special Forces and their support (airlift, supply, gate guards, etc) are rarely drawn from conventional warfighting units, but they still constitute a large number of soldiers, and a large piece of a limited logistical pie. The current conventional ground forces strength of the United States Army is 10 divisions and 2 Armored Cavalry Regiments (ACRs). Converted to easier terms, thats the equivalent of 32 combat brigades. However, that does not mean that 32 combat brigades are available to go to war. Two are committed to the Korean peninsula. Two at Fort Lewis are undergoing a massive equipment and doctrine overhaul, and given their recent performance at Ft Irwin are not likely to deploy anywhere. One brigade (1/4 Infantry) is a test-bed for new digital technology at Ft Hood and is also unlikely to deploy.
Two brigades are spread across the Balkans and another is based in Khandahar. Take out these brigades and that leaves 24. Now subtract the brigade training up for the Balkans, and the one that just got back and needs retraining before fighting a war; ditto with the brigade that just came back from Afghanistan. Then take out the two brigades in the Pacific that are designated reinforcements for Korea, and youre left with 19 combat brigades to go fight a war in Iraq and then occupy it for years, not months.
The Gulf War in 1991 was fought with eight divisions, plus two heavy ACRs (only one of the remaining ACRs is a heavy one, the other is HMMWV-based). That total is 26 brigades, and that was just to fight the war, not to occupy anything. And turning to the reserves will prove equally difficult, since most National Guardsmen signed up as a warfighting reserve for the country, and while they have no objection to chasing the Republican Guard around the desert, how bad will retention in the reserves be when those soldiers are asked to put their lives on hold for years, not months to occupy a conquered Iraq.
Either the Bush administration hasnt done their math well, or they just dont care, but, simply put, conquering Iraq, and then occupying it for years, not months is not something that they have enough soldiers to do.