One of the more compelling arguments against any further U.S. intervention in the civil wars in both Iraq and Syria is that these conflicts have been brewing for some time. They are one part religious civil war – the Sunni/Shia divide very similar to Christian/Protestant battles after the 15th Century – and another part battle for territory.
As has been noted by many major outlets, but perhaps most interestingly by The Atlantic, there is a group of residents in Northern Iraq who do not identify themselves as Arabs: The Kurds. In an agreement with al-Maliki, the area of Iraq known as Kurdistan (a territory the total of which encompasses parts of Turkey and Syria as well) is relatively autonomous. They have their own military and, perhaps more importantly, a stable economy.
The Kurdish Regional Government is currently dealing with companies like Exxon and Mobil, selling them crude oil independent of Baghdad oversight. According to CNN, “proceeds [from these oil sales] are held in a Turkish bank; the Kurds say they will take 17% and the Iraqi government is entitled to the rest.”
In Iraq whoever controls the oil fields controls the economy. The Kurds have a significant percentage of the oil – during my time in Iraq, insurgents would often attack these oil fields and trying to set them ablaze in the night – but the areas ISIS first claimed was the oil-rich part of Iraq.
This is the reason that these countries simply don’t split up into their pre-World War I configurations, when ethnic tensions were not at the boiling point they are presently. The ability to produce oil, and thus have a robust economy, is not equally distributed throughout ancestral lands. They are not content to simply reclaim their ancestral lands, they now want it all.
We will never know if al-Maliki would have stoked sectarian tensions if the U.S. had left behind even a token force. Despite what you may have heard, the requests to reduce troop numbers came from al-Maliki, not President Obama. So while the current situation may have been aided in one way or another by the departure of U.S. troops, the conflict was inevitable.