Problems in the post-IS phase will be more varied and complex than the fighting against IS itself, and solutions will probably be harder to find. The parties involved have diverse and conflicting regional associations.
This diversity includes nationalist forces with separatist ambitions, such as the PKK and to a lesser extent Barzani’s KDP; religious forces such as Shiite militias like the Hezbollah Brigades and Asaib Ahl al-Haq that have an ideological alliance with Iran; and zonal factors such as the tribal forces led by Sheikh Ahmed Abu Risha in Anbar province, which have regional ambitions to liberate their areas.
It could be that the real war in Iraq has not even started yet. The moment IS is defeated could mark the start of the comprehensive collapse of Iraqi identity. This is a possibility since the political entities that formed following the 2003 invasion of Iraq — such as the Dawa Party and the Islamic Supreme Council of Iraq — have not succeeded in laying a foundation for unity.
The parties involved agreed to put aside their accumulated differences and conflicts to focus on battling IS. This has created two new challenges. On one hand, some groups’ differences are re-emerging as areas are being liberated. On the other hand, new political and military forces have been formed that did not previously exist or were not as effective as they are today.
There's an old saying about different factions who are at odds with one another but at the same time are at war with a common enemy "The enemy of my enemy is my friend!"
However once the common enemy is defeated the "STUPID" factions resume their differences with one another. Are you people that stupid that you learned nothing when fighting your common enemy. You just finished working together towards a common goal. Why can't you keep doing that? You're like little children playing in a sandbox. The sand is there for everybody. No one is entitled to all the sand for themselves. Learn how to share and how to respect one another. Remember: A donkey who is stubborn does not get fed.