To the extent that the United States has any interest in the regions, it cannot act with direct force. Instead, it must act with indirect force by using the interests and hostilities of the parties on the ground to serve as the first line of containment. If the United States intervenes at all, it will do so by supporting factions that are of interest to Washington. ... In Iraq, it would mean applying sufficient force to prevent the annihilation of any of the country's three major groups, but not enough force to attempt to resolve the conflict.
That's basically why I wanted to keep troops in Iraq after 2011. Our presence would prevent any parties from going outside of politics to wipe out their opponents, and keep outside powers from supporting one faction to achieve a violent victory.
With the safety net of survival in place, the groups could negotiate deals. We don't need to suppress the divisions with violence as Saddam did. Just make the divided factions keep competition within peaceful means.
Like I've said since January, send Biden to Iraq and keep him there until there is a deal among the parties to fight the ISIL invasion.