The caliphate cracks

That may help explain signs of internal tension. The movement has started to kill its own followers, sometimes for fleeing before the enemy and on at least one occasion supposedly for zealously beheading too many people. Residents complain of extortion, violent repression and declining public services. There are reports of tensions between local and foreign members over disparities in pay.

Judged by its own standard, then, the caliphate is failing as an all-conquering state and model for society. That matters because a proto-state with a large territory and population to defend is also more vulnerable to setbacks than terrorist groups that are not rooted to a patch of land. Precisely because IS claims to be running a model Islamic state, its visible failure exposes the bankruptcy of its ideology and the hollowness of its claims to would-be recruits. If, as some say, the secret of IS’s success is success itself; then failure will gain momentum, too.

Even so, the hardest part of defeating IS still lies ahead, starting with the military campaign in Iraq. In recent days the operation to oust it from Tikrit has been hampered by hidden bombs and snipers. And after Tikrit falls, there is Mosul—bigger and more important, with a population closely associated with IS. The recapture of Mosul is vital to puncturing IS’s claim to be a caliphate. The nature of the campaign matters, too. The Iranian-sponsored Shia militias at the forefront of the fighting in Tikrit are known for having victimised Sunni civilians in earlier fighting nearer Baghdad. The fear is growing that, by depending so heavily on Iran, Iraq is being turned into an Iranian satrapy. If so, Iraq’s disenchanted Sunni population will cleave even more tightly to the IS jihadists as their best and only protectors. It is important, therefore, that the attack on Mosul is led by a professional, non-sectarian Iraqi army. The trouble is that the Iraqi army is demoralised and far from ready.