The world has rightly been horrified and fixated by the Islamic State (ISIS), for three reasons.

First, ISIS’ barbarism knows no limits. Beheadings, crucifixions, ethnic cleansing and mass slaughter make ISIS one of the deadliest collections of psychopaths the world has known.  

Second, ISIS isn’t a terrorist organization; it’s an army, and it’s growing rapidly. Latest CIA intelligence puts ISIS’ headcount at between 20,000 and 30,000. Its reputation is so fearsome, many of its opponents simply defect to its ranks, like kids joining the toughest gang in school just so they won’t get picked on.

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Third, compared to the complexities prevalent elsewhere in the Middle East, ISIS and its actions are easy to understand. It has mobilized to grab land in western Syria and northern Iraq. 

If successful, it will establish a Sunni caliphate that will make Saudi Arabia and Taliban strongholds in Afghanistan look like liberal communities. It will become the biggest recruitment ground for fanatics who will target the Middle East and lands north, south and west of the region.

No doubt, letting ISIS continue to run amok would be catastrophic, but let’s put the current threat in context.

ISIS’ army has some degree of training and skill, but how would it fare against the expertise and professionalism of an American, British, French and Australian force whose infantry headcount combined is in excess of 825,000 fulltime soldiers?

It is a rhetorical question, and those nations and others steadfastly refuse to put their soldiers’ boots on the ground in Iraq and Syria. Instead, President Obama and his allies prefer the tactic of using airstrikes to combat ISIS.

This week, The United States, and other countries including Sunni Arab states, have bombed ISIS bases in Syria and Iraq.

But airstrikes alone won’t defeat ISIS.

Much like pouring boiling water into an ants’ nest, airstrikes will kill some, but scatter the rest. We don’t want ISIS members scattered, because they will regroup.

The Iraqi army and non-extremist Syrian rebels are fighting ISIS on the ground and are being given weapons and supplies by the U.S. and other nations. They face a daunting task and need more help than they’re getting.

If Obama can’t tolerate U.S. boots on the ground in Iraq and northern Syria, he still has an almighty sledgehammer at his disposal: the CIA, NSA and other special operations agencies and units.

Core to their work is the collection of intelligence from which decisions can be made about action. This can and must be a key strategy in defeating ISIS.

In its simplest form, this strategy includes identifying ISIS troop movements and bases of operations. At the more complex end of the spectrum, it includes neutralizing sources of ISIS funding and plugging the exodus of Western jihadists who want to join the ISIS cause.

Intelligence collection is not the only activity that’s in the bloodstream of the CIA. In times of war, the agency is adept at disrupting and destroying its enemies. It does this through a variety of means, including rallying and mobilizing local resistance cells; destroying supply chains; using information and misinformation to diminish support for the enemy and create confusion; and assassinating key enemy leaders.

The CIA’s potency is enhanced by virtue of the fact that it is not a visible army. It strikes unnoticed, and no enemy likes being hurt by an invisible opponent.

But Obama doesn’t trust the CIA and the NSA.

He’s criticized both agencies and distanced himself from them because of their recent use of torture and surveillance of U.S. citizens. Regardless of one’s views on waterboarding and PRISM, the way both agencies were publicly vilified by the president and his administration has created low morale in the U.S. intelligence community.

No doubt the CIA and NSA are playing a role in combating ISIS, but the president won’t let them work to their full potential. Instead, he prefers to keep them on a short leash.

Obama’s strategy to use U.S. airstrikes in support of local Arab military units may ultimately defeat the ISIS army. The problem with the strategy is it won’t obliterate every ISIS soldier. Instead, thousands of former ISIS members will return home and continue to wage their war on Western values.

We will be their targets.  

Matthew Dunn was a former MI6 officer who worked in hostile locations around the world. He is the author of the espionage novels "Slingshot," "Spycatcher," "Sentinel," "Counterspy," "Dark Spies," "Spy House," and the forthcoming "A Soldier’s Revenge" (William Morrow). For more information visit matthewdunnbooks. You can also follow Mr. Dunn on Twitter @MatthewHDunn and find him on on Facebook