Is anyone still wondering why Bush 41---who's forgotten more about world affairs than his son ever learned---left Saddam in power after liberating Kuwait? For all of the bad advice W got, the best advice he could have received was from his Dad, and he didn't listen to it
When you have a country made up of ethnicities/cultures who historically hate each others' guts, only a brutal dictator can hold it together--look what happened in the Balkans after Tito died.
That being said--a reckoning with Iran has been brewing since 1979. Now that we've removed the natural counterweight to their influence in the region, it's inevitable that our military will have to pay that price. The day we leave Iraq, is the day the Revolutionary Guards march south, and it plays out just like Tom Clancy depicted it in one of his books--a "United Islamic Republic" and the whole region goes kablooey.