We knock a few legs from out under the table, to allow local neighborhood types to manuevuer. We have a vested interest in defeating ISIL, however, we do not own the fight. Create enough space to allow the local players to move, and we’ve done our part. Scope creep is always the danger. There is no victory for us, just influence.
We’ve been over there for at least 16 years!
Also, I think we’ve learned that a secular despot, as despicable as they are against humanity, is far less of a threat to the US, as is a power vacuum that allows radicals in. A complete solution is up to the folks that live in the neighborhood, we just need to ensure the struggle remains in the neighborhood.