I often hear that it is not possible to defeat an enemy with air bombardment alone. I have a lot of trouble understanding how this can be the case. If you set fire to every square millimetre of ground using napalm, phosgene, chemical, biological and nuclear weapons, surely there would be a reasonable probability of annihilating every single individual member of the enemy? I think it was on Okinawa in WW2 that the bombardment was so intense that even the soil and rock turned molten. Is this approach in Syria/Iraq just not practical? Is the materiel needed too costly? I know they occupy some 15,000 square miles but surely the vast majority of that land could be incinerated? The enemy could be snuffed out in under a week if we really wanted to.
ISIS, and every living thing in the area, including civilians. Not all of which, at any rate, are supporters of ISIS. They just happen to be in the wrong place at the wrong time.
As another point, you could consider that there hasn't been a single bombing campaign in history that, on its own, was responsible for winning a war (with the possible exception of the nuclear bombs, and even that one is debatable). The carpet-bombing in WWII, napalm in Vietnam, etc etc. It doesn't work. Bombing can only be part of a military campaign, not the entirety.
Bombing tends not to take all your enemy out, plenty get missed to remain a force. Groups spread out and the cost become prohibitive. Under a week is wishful thinking.
But it can take out resources, deprive their war machine, leaving them less effective and vulnerable to troops when they are finally committed. If the will is there to finally commit them that is.
Bombing or troops on ground, it is all about killing or getting killed. No one wins war. It is a matter of who killed more. Humanity is not about killing but living and letting others live. But unfortunately a few countries do not believe in live and let live, they instead believe in live and kill. And that does not help in a real life scenario.
In an ideal world you are correct. In a practical one, one must stand up to those violently taking control and imposing their will on others. United the nations stand, divided they fall: and fall they must if they ignore deteriorating situations.
and here,
"The data released by Clinton shows the total payload dropped during these years to be nearly five times greater than the generally accepted figure. To put the revised total of 2,756,941 tons into perspective, the Allies dropped just over 2 million tons of bombs during all of World War II, including the bombs that struck Hiroshima and Nagasaki: 15,000 and 20,000 tons, respectively."
http://japanfocus.org/-ben-kiernan/2420/article.html
Even if they 'turned Syria to glass'(probably impossible gung-ho nonsense) before anyone could escape, the Rent-a-Jihadi have multiple geographic locations and next door in Iraq is one of them.