Though they have, throughout US involvement in the Syrian War, been America’s go-to ally, the Kurdish YPG hasn’t had the rosiest of track records. Several times throughout the war, when offensives have put them in control of Sunni Arab territory, they have engaged in ethnic cleansing, killing Arabs they see as “pro-ISIS” and burning entire villages worth of homes.

This is informing the almost exclusively Sunni Arab population of the ISIS capital city of Raqqa as the YPG launches a major offensive just north of the city, and according to locals, is prompting many civilians to join the ISIS effort to defend the city.

This problem has been true in ISIS territory in both Iraq and Syria, where at times the “liberators” have been seen as unwelcome, and prone to violent outbursts against the locals. In Raqqa, the historical distrust between Arabs and Kurds is punctuated by a large influx of Arab refugees last year when the Kurds took nearby Tel Abyad.

The reality that many locals are indeed siding with ISIS, over fear of the alternative, is likely to only add to the tendency for the fall of ISIS territory to be followed by bloody purges of civilians as collaborators.