Well, I wanted to be a military historian, but then I actually got a job doing history as a B.A. and I never went back to school--I was too busy actually doing it to go back and learn it. Not military history--other history, but all other history is strongly affected by warfare, so you never really get away from it.
There are thought to be
fourteen "enduring" bases being built in Iraq, though the locations of two of them are not known. They're probably finished now, as it's obvious that nothing else has been worked on since 2004. China had a role in delaying the construction; they produce most of the world's
cement, and when they discovered what the Americans were up to, they decided to put that cement into their own enormous works projects at home, which created a worldwide cement shortage. So it's safe to assume that those bases are... substantial, and no doubt very expensive.
Fourteen--or twelve--bases is a pretty significant number. Modern "bases" are really just fortresses. They don't look like castles, but they do the same thing: you can house a lot of troops in there if you want, but you can defend it with comparatively few if those other troops are off doing something else--like invading Iran. In this case, each base is probably built to hold a brigade (say, 3000 troops) or more, but be defended by a battallion (about 400-500 troops) while the
REMFs and Halliburton employees hole up inside. They can be resupplied by air if necessary.
There are three or four divisions in Iraq, or between 15 and 20 brigades, and each brigade is made up of between two and seven battallions. Thus two brigades, or one rump division, can theoretically hold all of those bases while the other two or three reinforced divisions in Iraq can move on to other projects.
Like I said, things would instantly go to hell in Iraq if the Americans pulled into their shells, but seriously, does anyone really think that we give a damn at this point? The purpose of invading Iraq was to prevent it from supplying cheap oil in exchange for euros, and that purpose won't be defeated by allowing people to riot. (The Iranians recently moved their medium of exchange from dollars to euros, one more really good reason to suspect that we'll be stealing their oil sooner rather than later.)
In fact, we can expect the Bush Administration to cite the predictable unrest as all the more reason to stay there forever.