Vacuums are created when societies are drastically destabilized. That can happen due to a financial collapse, a revolution, a lost war, a great natural catastrophe, or a foreign invasion...or several of those in combination.

Iraq was once the most modernized and socially progressive Arab country in the Middle East (and under Saddam Hussein too). It then became gradually destabilized and ruined by a number of events:

1. The massive arming of Saddam by the USA and other countries, in order to attack Iran and police that general region for the USA.

2. Iraq's disastrous war with Iran in the 80's which killed an immense number of people on both sides and achieved nothing useful for anyone except arms dealers (many of those based in the USA).

3. Saddam's further reckless military ambitions after that (What do you do with a huge army that is sitting on its ass costing money?), which led to his foolish attack on Kuwait (given the green light by the American ambassador to Iraq at the time, April Glaspie).

4. The Gulf War, in which Iraq's army was crippled and partially massacred and their air force ceased to exist, and they lost sovereignty over most of their air space, and their economy was subsequently wrecked by sanctions, and they continued to be bombed for years afterwards.

5. And finally...George Bush's phony crusade to expose Saddam's "weapons of mass destruction", which turn out not to have even existed.

Result: A once rather modern and progressive Arab society has been turned into a vacuum by international political games aimed at destroying Iran's Islamic government and securing control of Iraq's oil.

None of it was done to help Kurds, Shiites, or any other victims of Saddam's autocratic rule. None of it. Saddam was first a handy USA hatchetman to kill Iranians, later a perfect excuse to wage an oil war.

None of this excuses Saddam for his own misbehaviour, but he is a mere bit player. The big players are oil companies and the US State Department and Whitehall.

The British were playing around in there a long time before the USA ever did, and doing much the same things. Just read a history of the region in the 20's and 30's if you don't believe me. They slaughtered people there. Oil is the name, and mass murder is the game.

If the USA pulls out now, will it create a vacuum? Yes. But the USA has ALREADY created a huge vacuum in Iraq in no uncertain terms. The USA has spent over 2 decades creating a vacuum in Iraq, and making the disintegration of that country virtually inevitable.

So I would submit that their pulling out now will only turn one kind of vacuum into another kind of vacuum, that's all. It will be an even more obvious vacuum. Will it be worse? For awhile, yes. You will probably end up with a Balkanization of Iraq into 3 separate regions, kind of like what happened with the former Yugoslavia.

What a mess.

You cannot break an egg with a sledgehammer and expect to magically repair it afterwards with a tube of crazy glue...