How did it come to this?

TENSION had long been mounting in Sunni-majority parts of Iraq. When it broke on June 10th, violence spread with the force of a flash flood in the desert. Within 48 hours of seizing Mosul, Iraq’s second-biggest city, Sunni rebels had barrelled down a 200-mile stretch of the Tigris river valley, scattering troops loyal to Iraq’s Shia-dominated central government and threatening Baghdad, the capital.

The surge was spearheaded by a fearsomely brutal, al-Qaeda-inspired group, the Islamic State of Iraq and Greater Syria (ISIS), but it was bolstered by a range of other armed Sunnis and was backed by many ordinary citizens. It has wrested the Sunni quadrant in the north and west of Iraq from government control. And it has driven a Sunni wedge between the Shia-majority south of the country and the autonomous region of Kurdistan in the north and east (see article). All but a wisp of the line of around 1,000km (621 miles) that separates the Kurds from the rest of Iraq now abuts rebel-held or -infested territory.