Terrorism & Extremism
Defeating the Islamic State will be the easy part. The hard part will be securing the peace, making sure that the forces converging on Deir Ezzor don't start fighting among themselves. The stakes for Deir Ezzor could not be higher. The Iranians want an overland route to the Mediterranean. The Kurds want a buffer between Assad's forces and their territory further to the north. In some ways, the situation is like the end of World War II, when Soviet and American forces converged on Berlin.
The US has flaked out on the Kurds in the past, so it's understandable that they're worried about US withdrawal in Syria now, but in this case, the US won't be going anywhere for a while. Once ISIL is defeated, the US will need proxy forces on the ground to push back against both Assad and Russia.
The image people often have is plane-loads of these [jihadists] flying out, but that’s the wrong image: It’s people filtering out in dribs and drabs.
What do you do when your allies [like Pakistan] are part of the problem? The desire to turn our backs on these people is there, but then you worry that terrorists will have more operational freedom and it will cost you more in the long run.