J.M. Berger is co-author of ISIS: The State of Terror and a nonresident fellow at the Brookings Institution’s Project on U.S. Relations with the Islamic World.

Over the course of the past year, many analysts and policymakers have struggled to pin down the terrorist capabilities of the Islamic State. As an insurgency, it had proved resilient. As a terrorist actor, projecting a threat outside its borders, it was unproven.

Several phases of denial have played out. Initially, some experts speculated that ISIL had no particular aspirations to execute spectacular attacks outside its borders. Then, some argued that Al Qaeda was more sophisticated than ISIL, and therefore posed the greater threat. Finally, the focus shifted to so-called lone wolf attacks, an area in which everyone eventually could agree ISIL excels.


All of these hedged assertions looked reasonable when compared with vague and irresponsible alarms from some quarters about the existential threat ISIL allegedly posed to the American homeland and the West in general.

But in a few short weeks, ISIL has flexed its terrorist muscles in an unambiguous manner. It claimed responsibility for the October bombing of a Russian passenger plane that killed 224. The group is also believed to have killed 44 people in a suicide bombing in Beirut just days ago. And after Friday night’s complex attacks in Paris—in which three teams of operatives employing guns and suicide belts killed at least 129 people and paralyzed the country—ISIL again took responsibility. In the months preceding all of this, ISIL had struck repeatedly around the world, in scores of small and large attacks, including a synchronized suicide bombing in Sana’a, Yemen, that killed more than 140 in March.

There will be many lessons to unpack in the days and weeks to come—and there are many details about the Paris attacks that we don’t yet know, including whether it was minutely directed from ISIL’s central command. But the most important lesson may be how fundamentally misunderstood ISIL’s capabilities, behaviors and intentions have been. While news reports in the wake of the Paris attack have talked about ISIL’s “escalation of capabilities,” what we are seeing is the deployment of assets that ISIL has held since it declared its caliphate in June 2014, even as the very definition of terrorist “capabilities” has become more and more diffuse.

In March, my co-author Jessica Stern and I argued in our book that we should not rule out the possibility that ISIL might have the capability to carry out spectacular attacks, even on the scale of 9/11, and I reiterated that warning during Senate testimony in May.

Our evaluation was not based on specific intelligence but, rather, on simple accounting. While exact numbers are elusive, ISIL has at least tens of thousands of fighters, most of whom are battle-tested, including thousands of foreign fighters. That is a far larger force of potential terrorists than Al Qaeda possessed when it carried out 9/11 (likely well under 1,000). ISIL can easily staff a spectacular attack; in fact, it has had that capability for well over a year.

ISIL also has money. Again, specific and credible estimates are wanting, but based on its estimated peak wealth in 2014, the group today is believed to have tens of millions of dollars in reserve, and more likely hundreds of millions. In comparison, Al Qaeda incurred about $500,000 in direct costs for the 9/11 attacks, so funding a spectacular attack is also within ISIL’s reach, and has been for well over a year.

Since 9/11, the landscape has changed in other ways as well. ISIL has expertise using the new technology of social media, which allow it to sift through hundreds of millions of users in search of a few thousand who will support and abet the group’s activities.

Despite all of this, the question of skill, or “sophistication” as the pundits like to call it, may have led astray many analyses of ISIL. Al Qaeda was obsessed with ingenuity, following in the footsteps of legendary jihadist bomb-maker Ramzi Yousef. The clever design of Al Qaeda bombs and the group’s propensity for intricate plotting gave counterterrorism officials plenty of shiny objects to chase.

When Al Qaeda tried to deploy liquid bombs against U.S.-bound airliners in 2006 (modeled after Yousef’s designs), the United States realigned airport security around the threat. Armed with technology and a large line item in the homeland security budget, we chased the shoe bomb and the underwear bomb and the printer bomb—all of them ingenious, and all of them failures.

Al Qaeda’s love of elegance was a distraction. Did ISIL have a diabolical genius like Ibrahim al Asiri, the underwear bomb-maker of Al Qaeda in the Arab Peninsula? No? Then perhaps AQAP was “the greatest threat to the U.S. homeland,” as The Heritage Foundation noted in January, and the American Enterprise Institute argued in September, echoing a great many other assessments from terrorism analysts and government officials.

AQAP does present a threat, of course, as amply demonstrated by the attack the group spearheaded at the Charlie Hebdo offices in January. But in the meantime, ISIL (we currently believe) was preparing to infiltrate an insider at the airport at Sharm el-Sheikh, Egypt, obviating the need to disguise a bomb as a convincing houseplant: On Oct. 31, Russia-bound Metrojet 9268 exploded and crashed, killing more airplane passengers in one blow than AQAP managed in years of trying.

Terrorism is inherently improvisational. An attack can be simple from start to finish, such as ISIL supporters’ lone wolf attacks in Canada in 2014. Or it can be complex in its ambition but technically simple, incorporating guns and using relatively well-established explosive technology, as currently appears to be the case in the Paris attacks.

Further complicating matters, AQAP was also perceived as being the most committed of all jihadist groups to attacking the West in general and the United States in particular, in part because of its English-language magazine, Inspire, which combined practical bomb-making advice with ideological incitement.

But in reality, AQAP carried out only a handful of attacks, and at a languid pace, over the course of many years. It spared one trainee for the failed underwear bomb plot on Christmas Day 2009 and two operatives for the Charlie Hebdo attack. It boasted of spending just $4,200 on the 2010 UPS bomb plot, in which a bomb disguised as a printer toner cartridge was smuggled onto a cargo plane and intercepted before detonation.

This activity was far from trivial. Much of it was lethal, and the plots that failed could have been deadlier still. But all of this activity made use of a fraction of the resources held by AQAP, one of the largest and best-funded Al Qaeda affiliates. It was clear that AQAP was far more focused on its local insurgency in Yemen than on the “far enemy.”

Of course, after ISIL seized Mosul in June 2014, it similarly was perceived to be focused on waging war at home and establishing its purported caliphate. While this perception was not incorrect, it was incomplete. When the West took a kinetic interest in ISIL’s activities, in September 2014, the group responded with provocations, starting with the grisly videotaped murders of Westerners taken hostage in Syria.

There was scant reason to hope these provocations would stop when ISIL’s supply of hostages ran out. In response to every threat, the group has responded with more and more intense provocation. When Jordan joined the American-led coalition against ISIL in September 2014, ISIL responded by burning a captured Jordanian pilot alive. And when Russia began airstrikes in Syria earlier this fall (albeit with more bark than bite), ISIL, it appears, took down a Russian plane.

As the group faces growing pressure on its holdings in Iraq and Syria—losing Sinjar to Kurdish forces just hours before the Paris attacks—ISIL will continue to seek ways to change the conversation and preserve its image of strength. And if the coalition succeeds in dislodging ISIL from its primary geographical strongholds, it will free up thousands of fighters to take up new roles as terrorists in more far-flung places, a prospect that most in the West are probably not adequately prepared to face.

We should also remember that while advanced training and ample resources come into play in a terrorist group’s capabilities, perhaps the most important assets to a terrorist plot or a mass murder are patience and discipline, qualities we can do little to prevent people from developing.

These days, almost anyone has the “capability” to kill and maim dozens of people with little or no support—the Tsarnaev brothers in Boston, Dylann Roof in Charleston, Adam Lanza in Newtown. The game-changing precedent was set in 2011, when Norwegian right-wing extremist Anders Breivik managed to bomb a government building and then slaughter 77 people, mostly children, all by himself, without any outside funding or specialized training.

Spectacular terrorism no longer requires spectacular resources. A few outliers in a world of 7 billion people can wreak tremendous havoc. When those few can find like-minded people across wide geographies who reaffirm and tangibly support their desire to kill, the stakes only rise.

The technology of killing may have vaulted past our ability to process and understand the problem. Although ISIL is the vanguard of this new style of organization, it will not be the last extremist group to exploit these dynamics. Even as we try to measure the proportionality of our response to an attack, our evaluation of terrorist capabilities must open to an ever-wider array of possible disasters from an increasingly diverse group of adversaries. It will not be easy.