ISIS is in an interesting position: they hold territory, and therefore have an infrastructure, logistics and operations network they need to maintain. It’s all well and good to get 500 Toyota trucks with .50 caliber machine guns on them to overrun a town. It’s quite another to fight the Syrian Army.
Between Raqqa (Al Raqqah on the map, in the top leftish area) and Mosul (top towards the right side), ISIS snagged huge stockpiles of weapons and ammunition. While it’s relatively easy for ISIS bring money into their boundaries to pay their foreign fighters $1,000 a month to $150 a day, it’s harder to get spare parts and maintenance gear into their area. And sure, they’ve got jets captured from Syria. Question is, how ready, after three years of war and sanctions against Syria, are these planes to get into the air? And do they have pilots with the skills to fight real air-to-ground engagements? Eliminating these stockpiles, including fuel depots, is the first of the one-two punch.
So that’s the reason for the air war. However, not to flog a dead equine, the air strikes are essentially meaningless to breaking ISIS as a force. For that boots on the ground need to go house-to-house, weeding the ISIS chaff from the civilian wheat, throughout this double-damned part of the world.