We have an example of war crimes tribunal after WW2. The evidence now remains in Syria and surrounding countries together with surviving witnesses. The obvious thing to do is for the international community to fund the infrastructure to bring justice to the ”Citizens of the Caliphate” and to let the Kurds manage them from international funding. If ISIS had succeed they would still be out there imposing death and destruction towards the rest of the World.

The problem of returning Jihadists who themselves had been radicalised:

Belgium: Joining the Jihad | European Journal

Also:

This video is set in Aceh, one of the areas destroyed by the Boxing Day Tsunami of 2004 where the world took pity on the survivors of this huge devastation and who had donated funds towards the reconstruction of the whole affected area. It has been said that the local fisherman who inhabited the beach line were never to return but instead money was lavished on luxury hotels in the vicinity. A Muslim civil war had also raged but was brought to an end by this tragic occurrence and as part of negotiations the rebels were given Aceh to practice their Sharia Law as they felt fit. The fact that the Mosque was the only standing building to survive was taken as a sign from their God but in reality it would remain standing because it was a very substantial building, unlike those in the surrounding area, and also it can be seen that the windows gave out under the pressure of water which then was able to flow freely inside the building through what now appear to be a building built on stilts. Instead of feeling sorry for those who lost their lives or their worldly good it has been interpreted as a judgment on the people which then serves as a justification for the imposing of Sharia Law.

Towards the end of the video it can be seen that there is a developing sympathy the the type of cruel extremism which has been well documented in Syria, Iraq and Afghanistan.