Using its own version of “soft” and “hard” power, the Islamic State is crushing resistance across northern Iraq so successfully that its promise to march on Baghdad may no longer be unrealistic bravado.

While conventional states try to win hearts and minds abroad before necessarily resorting to military force, the jihadist group is also achieving its aims by psychological means – backed up by a reputation for extreme violence.

The Islamic State, which in June captured a vast stretch of territory in the north including the largest city Mosul, used this strategy when its fighters met armed resistance from the town of al-Alam for 13 days running. […]