the whole point of delineating societal groups is to provide ring-fences for cultural groups that may otherwise be at each other's throats. Just look at the continuous fighting between Shi'ite and Sunni muslims that could arguably be traced back to the Sykes-Picot agreement drawing up borders that did not respect the locations of mutually-unfriendly groups.
Slight nitpick: The Shia-Sunni divide has plagued the Islamic world ever since the succession of Muhammad. Sure, Sykes-Picot aggravated it greatly, but it did not cause it.
