The Bush administration seems to have thought that Saddam would be displaced, Iraq subdued, and the UN put in charge as the US moved on to other tasks — like a show down with Iran. But the UN headquarters in Iraq and the designated national administrator were blown up and the insurgency was on. In that manner, we got stuck in Iraq, eventually to downsize and let Shias loyal to Iran come into the control of most of the country.
It is hard to even refer to it as an “insurgency” when the Iraqis are simply fighting to remove foreign troops from their soil. BLM is an insurgency.