On the other hand, now you have huge displaced populations concentrated amongst each other that are highly heterogeneous. There has been cooperation so far, but what happens when it comes time for resettlement amongst the bones of the moribund Islamic State, with Sunnis getting pick of the land? Especially with a former metropolis like Mosul, with the minorities at their armed peak and waiting right in the wings behind the national forces? You just know there are going to be reprisals against Sunni collaborators or perceived collaborators, which will then reverberate throughout the region...
Ethnic cleansing has formed a bedrock for modern European peace only in conjunction with numerous political and economic factors, decades of careful compromise and reconciliation under the pressure of superpower dominance. I don't think this will be replicated in West Asia - and we may be moving out of this stage in European history anyway.
(And it's questionable how much stability cleansing Greeks and Armenians has rendered Turkey...)
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