Its gruesome tactics, as well as images of the black ISIS flag being waved in numerous Iraqi cities and towns, have dominated the media and pressed governments around the world to try to formulate a forceful response.
But a number of Middle East analysts say that despite its incendiary rhetoric and a widespread perception that its ranks are swelling, ISIS has far more enemies than allies and is unlikely to expand its reach.
"They are not invincible," says Kamran Bokhari, vice-president of Middle Eastern and South Asian affairs for the Texas-based geopolitical intelligence firm Stratfor.
Wayne White, who worked for several decades as an Iraq analyst for the U.S. government, says that the language used by Western governments and media to characterize ISIS has "distorted" the extent of the threat and "allowed public pressure to rise for radical solutions."
Spurred by the recent release of videos featuring the beheadings of U.S. journalists James Foley and Steven Sotloff by an ISIS member with a British accent, Western governments — including Canada's — have committed to greater action to try to stamp it out.
But White says the group is not the persuasive threat it's made out to be.
"I'm not saying it isn't dangerous — we all know its character and fanaticism. That's plain to see. But it feeds on weakness," says White, who is now a scholar at the Middle East Institute in Washington, D.C.
While its territorial gains are not insignificant, he says the areas ISIS has "gobbled up" are regions where it "found weakness." In other words, places where it was able to collaborate with local groups, "or places where Shia or Kurdish forces wouldn't really fight for those areas."
In fact, ISIS may have already reached "the extent of their growth, in terms of territory," says Clinton Watts, a former U.S. soldier and counterterrorism agent and now a senior fellow at the Foreign Policy Research Institute in Philadelphia.
"They can't push into the Shia areas in Iraq. They've pushed toward the Kurds, and that's when U.S. airstrikes started."
Social media savvy
One of the reasons ISIS seems so fearsome is that the group has been very adept at "psychological operations," says Bokhari.
The group has been especially savvy in leveraging social media, which it has used to spread its message, publicize its triumphs and recruit fighters from the region and around the world.
ISIS occupies large stretches of land in eastern Syria and northern Iraq, although not all of it is contiguous.
The sheer fact that ISIS claims to have established a caliphate is seen as a great achievement by jihadists worldwide, but it will be difficult for ISIS to make greater gains — or even hold its current ground — given its staggering list of enemies, says White.
Because of its radical, Sunni-focused interpretation of Islam and persecution of minorities, ISIS has come into conflict with Shiites — who comprise the religious majority in Iraq — moderate Sunnis, Christians and Yazidis, as well as the Kurds in the north.
ISIS's brutal, uncompromising tactics have also alienated fellow jihadis, says White.
ISIS shifted its focus from fighting the Syrian regime of Bashar al-Assad to gaining territory in Iraq after a falling-out with factions such as al-Qaeda splinter the Nusra Front.
Writing in Foreign Affairs magazine, global security expert Mohsen Milani says neutralizing ISIS "may even produce the previously unthinkable: co-operation between Iran and Saudi Arabia, two countries that have more or less fought an open proxy war for the past several years in Iraq, Lebanon and Syria."
As a result of all these enmities, ISIS has been forced to fight a battle on multiple fronts — against the Turkish and Syrian militaries near the Turkey-Syria border, the Kurdish peshmerga in Iraq's north, the Iraqi military and Shia militia throughout Iraq and U.S. airstrikes from above.
A multi-front war is a disadvantageous situation for any occupying force, says White.
'ISIS as a group is very small'
In terms of quantifying the threat, experts have said that ISIS fighters number in the tens of thousands. But Bokhari says the size of ISIS's membership is deceiving. He believes there are only about "3,000 to 4,000 core members."
"ISIS as a group is very small, but it's the alliances that they make that make them seem bigger," says Bokhari.
Among ISIS's few allies are about 5,000 members of the Baath party who were loyalists of deposed Iraqi dictator Saddam Hussein, says Bokhari. The two groups are united in their aim of rolling back the Shia dominance of Iraqi politics, which has been exacerbated by outgoing Prime Minister Nouri al-Maliki, who systematically alienated Sunni groups during his time in office.
But Bokhari says that the Baathists "are not committed ideologically and might be willing to throw [ISIS] under the bus" if a new government led by Haider al-Abadi is seen as more inclusive.
White says establishing an Iraqi parliament that is more representative of the different sects and ethnic groups in the country may be the single-most effective way of defusing ISIS.
That said, Watts at the Foreign Policy Research Institute warns that if it feels hemmed in, ISIS may trigger "an external attack" outside of the Syria-Iraq theatre.
There are already signs that something like that could happen. Watts points out that in May, Saudi authorities arrested 62 suspects in what was thought to be the first ISIS-related terror cell.
Watts says another "huge worry" is foreigners who have fought with ISIS in Iraq and Syria and may return to their home countries to foment trouble, a prospect that compelled British Prime Minister David Cameron to propose a law that would allow police to seize the passports of British citizens suspected of trying to support ISIS.
Watts says there is also a likelihood that "fanboys of ISIS," who may have never made any formal contact with Baghdadi's group, might choose to independently carry out attacks in the West on the ISIS's behalf.
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