The Sykes-Picot Agreement (1916)

The secret agreement between Britain and France to carve up the Ottoman Empire into spheres of influence drew arbitrary borders across the Middle East with no regard for ethnic, tribal, or religious boundaries. The resulting states — Iraq, Syria, Lebanon, Jordan — were artificial constructs that have generated a century of conflict. ISIS explicitly cited the destruction of Sykes-Picot borders as a goal when it declared its caliphate in 2014.