If in case you don't know the reasons why US troops can't leave Iraq

Here is my list:
1. Maintain the flow of oil and gas in the region.
2. Prevent the estabishment of an Al Qaeda safe haven.
3. Contain Iranian influence.
4. Prevent a regional war.
5. Maintain American military credibility in the region.
6. Prevent a humanitarian catastophe on the scale of Rwanda