On August 16, 2021, the world watched in awe as the Taliban marched into Kabul unopposed and nonchalantly shot photos in the Afghan presidential palace. The group’s rapid seizure of territory and capture of Kabul so stunned the world that the United States failed to evacuate thousands of its Afghan allies in time (though it did get some 120,000 people out before leaving). But the Taliban’s lightning advance should not have been a surprise. Despite an entrenched tendency to conceptualize jihadist groups as intrinsically irregular combatants—born out of two decades of US military experience during the post-9/11 wars—several such organizations have demonstrated a capability to effectively adopt conventional warfighting methods.

As I detail in my new book, the Islamic State (IS) group achieved similar feats in its military campaigns several years earlier, marking a decades-long culmination of jihadist conventionalization, or adaptation of jihadist fighting styles to conventional warfare. The jihadist ideology has always sought the establishment and preservation of a caliphate by force, necessitating the development of robust conventional warfare capabilities to seize and defend territory. The case of IS reveals the most important characteristics of this jihadist way of war and how to fight against it. It also illuminates major lessons about the future jihadist threat and how the United States can more effectively work with its allies to meet it.

The Islamic State Way of War

The IS way of war developed out of an ideological divergence between IS and its former parent organization, al-Qaeda. Having witnessed the swift demise of Afghanistan’s Taliban regime following the 2001 US-led invasion, al-Qaeda head Osama bin Laden urged his followers to refrain from openly holding territory and confronting larger, more advanced forces like the US military until their adversaries were sufficiently weakened and the jihadists gained enough public support. Nonetheless, the foundational jihadist principle of tamkin (a degree of empowerment that, in this context, enables consolidation of land to govern) proved stronger in the minds of al-Qaeda affiliates than their leader’s advice and it would remain the norm for jihadist groups to attempt to hold territory through campaigns of conventional warfare. Such was the case with al-Qaeda-affiliated groups in Iraq, Mali, Somalia, and Yemen. IS, developing out of al-Qaeda’s Iraqi affiliate, ventured further than any other jihadist group, taking on an apocalyptic outlook and labeling al-Qaeda and its supporters apostates for delaying the return of the caliphate. Indeed, IS saw the caliphate as not only its vision of a just society based on sharia (Islamic law), but also the base of the supposed forces of good against the antichrist in an imminent apocalypse.

With this sense of urgency, IS went about devising a strategy for seizing the considerable territories it would need to build its caliphate. The group’s early-2013 entrance into the ongoing Syrian civil war marked its definitive shift toward conventional warfare, and patterns in its operational style began to emerge. Four variables informed the IS way of war: organizational innovation, shaping operations, will to fight, and retention of the initiative.

Organizational Innovation

The 2012–14 period featured extensive reorganization and expansion of the IS military (the group was known at this time first as the Islamic State of Iraq and later as the Islamic State of Iraq and Syria). Most significant were the group’s creation of battalions, each with 300–350 fighters, all governed by a formalized bureaucracy called the Department of Soldiers and an improved military industry apparatus under its Committee for Military Manufacturing and Development. This augmented organization enabled the group to grow exponentially, absorbing more than forty thousand foreign fighters from over 110 countries and bringing its total numbers of fighters and their dependents possibly into the hundreds of thousands. The new arrivals often came with technical education and military experience that helped further boost IS military capabilities. At the same time, the group’s expanded military industrial capacity allowed it to build small arms, mortars, rockets, and—most importantly—suicide bombs on a large scale with a high degree of standardization.

High explosives production and other innovations fueled IS’s most important battle tactic: the frequent use of suicide car bombs (SVBIEDs, or suicide vehicle-borne improvised explosive device), often so heavily up-armored that they were nearly impervious to small arms fire and RPGs. The group used these SVBIEDs as shock weapons followed by a light infantry assaults. On the offensive, IS deployed SVBIEDs much like a regular army might use artillery or airstrikes—to soften up and demoralize targets in preparation for or close support of a ground assault. Exemplary of this tactic were IS attacks on Menagh Air Base (August 2013), Tabqa Airbase (August 2014), and the Ramadi city center (May 2015). On the defensive, IS frequently used SVBIEDs and follow-on light infantry advances in brutal tactical and operational counterattacks, particularly in eastern Mosul (October–December 2016) and, as I recount in my book, throughout the Hajin pocket along the Euphrates River in northeastern Syria (November 2018–March 2019).

Shaping Operations

Key to IS military success was the group’s ability to weaken targets before engaging them in combat. As Craig Whiteside has shown, a flexible tribal engagement strategy, hostile to some Arab tribes and conciliatory with more amenable ones, facilitated IS gains particularly in Iraq’s Anbar province by winning a degree of acquiescence and support from tribes that could have blocked the group. One example is the mid-2014 IS alliance with the Albu Karbuli and al-Salmani tribes against the more hostile Albu Mahal in al-Qaim in exchange for plunder and governance responsibilities. In contrast, as at Haditha, tribes and local populations that remained staunchly opposed to the organization largely held out against IS attacks, though jihadist assassination campaigns against hostile tribes, such as the Albu Nimr, at times helped tip the balance in IS’s favor. Infiltration of enemy security forces and insertion of sleeper cells were additional effective shaping tactics that helped cause Iraqi units to collapse during the IS assault on Mosul in June 2014 and a year earlier at the IS-orchestrated Abu Ghraib prison break. In defensive operations, IS shaping capabilities were much diminished over time, especially when it could no longer plan to attack targets far in advance and had to invest resources in preparing to meet adversary offensives. This helps explain why IS was far less successful in defending its territory than it was in seizing it.

Will to Fight

The most essential and consistent characteristic of the IS way of war was the high will to fight of its fighters along with a preference for engaging significantly demoralized foes. Shaping operations, coupled with information warfare and high IS determination, aimed to maximize the morale differential between IS and its adversaries so that when combat ensued, the latter would already be so brittle that victory would come quickly. American veterans of battles against IS remarked to me that IS fighters showed consistently high levels of determination and rarely fled or surrendered in disarray. Azad Cudi, a member of the US-backed People’s Protection Units (YPG), even recalls an instance of foolhardy jihadist determination at the battle of Kobane (September 2014–March 2015), with fighters reinforcing a position no less than four times despite airstrikes vaporizing it each time. IS won major, quick gains when it achieved a wide morale differential and suffered when it could not. Indeed, with some exceptions (like the sixteen-month IS offensive on Ramadi), the group’s most significant victories were won in a matter of days or weeks; getting bogged down against a determined foe or in a defensive posture forced IS to rely more heavily on the inconsistent tactical combat proficiency of its fighters, which reduced their success even though these fighters would mostly stand their ground and fight to the death unless they decided to retreat.

Retaining the Initiative

With organized, highly determined fighters and weakened adversaries, taking the initiative and keeping enemy forces on their toes was essential. Accordingly, IS fighters generally fought aggressively, with high mobility and frequent fighting patrols. This aggressive style kept IS adversaries constantly guessing, often paralyzing them, as at Ramadi in early 2015. Michael Knights and Alexander Mello aptly characterized the IS operational style as “tactical restlessness,” an “almost pathological need to take the initiative and attack the enemy. This approach can and does help sustain morale and extend the operational experience of surviving troops, but it also tires troops and continually erodes overall force strength.” The resulting self-attrition of the IS operational style is further reason for IS to prefer fast-paced operations, and its persistence even on the defensive ultimately contributed to the group’s inability to win virtually any defensive battles, when its enemies held the initiative. Moreover, an intensifying air campaign from late 2014 onward considerably reduced the organization’s mobility and exacerbated the self-attritional effects of its aggressive approach, notably at Kobane.

Assessing the Current Jihadist Threat

Although IS is now deprived of its territories in Iraq and Syria, its style of conventional warfare was on display with the Taliban’s recent recapture of Afghanistan. The rapid weeklong offensive culminating in the fall of Kabul followed months of surrenders to the Taliban, negotiations with tribes to acquiesce to the group’s rule, and buyoffs of police and militias as US forces departed. These efforts were strikingly similar to the IS tribal engagement campaign in Iraq. Where the Afghan army had a presence, the Taliban infiltrated its ranks, assassinated important military figures, and threatened soldiers’ families to instigate desertions, just as IS had done to Iraqi security forces. Demoralized by the American withdrawal and without hope for reinforcement, any remaining army units collapsed quickly and the Taliban entered Kabul without any fighting, reminiscent of the fall of Mosul to IS in less than a week. Hence, the Taliban’s aggressive retention of the initiative in a fast-paced, merely weeklong nationwide offensive after such a sweeping shaping campaign resembled—likely inadvertently—the IS style of territorial acquisition, indicating the emergence of an increasingly effective jihadist way of war.

In its former territories, IS has reverted to an insurgent posture, but is re-conventionalization possible? On the organizational front, the group’s ranks in Iraq and Syria are decimated, down to only ten thousand according to the latest US Department of Defense estimates. At the same time, the group has maintained a steady pace of attacks since 2019, including complex high-casualty strikes such as a bombing in Baghdad in July 2021 and regular deadly ambushes in Syria’s Badia desert region on forces loyal to embattled dictator Bashar al-Assad. If Assad regime forces are unable to retain control over the Badia, that region could become a flashpoint for IS recruitment and territorial rebuilding, with IS already performing shaping operations there like extortion and intimidation of locals and tribal communities. Despite considerable Russian and Iranian military support and access to armor and airpower, the regime has recently made virtually no progress against any major rebel faction, raising questions over its forces’ morale and continued willingness to fight. With morale and some shaping activities in its favor, IS might use a small territorial enclave (in the event of a reduced regime presence) in the Badia as a base for organizational rebuilding and future conventionalization.

Moreover, IS might attempt larger operations at al-Hawl refugee camp or prisons holding IS fighters in northeast Syria under the control of the US-backed Syrian Democratic Forces (SDF). The camp holds some 59,000 people, including an estimated 8,555 individuals linked to IS per camp administration statistics, while SDF detention centers hold thousands of IS members. The camp’s horrendous conditions, as well as IS efforts to enforce its extreme interpretation of sharia in the camps, like punitive killings, leave camp residents more vulnerable to radicalization and cooptation by IS. A significant escape from al-Hawl or the prisons would help replenish the group’s ranks and reenergize its conventionalization. However, the SDF—with vital US support—has managed to keep IS activity down, and attacks in SDF territories are considerably less lethal than those in regime-held ones. Also, a large SDF counterterrorism operation in al-Hawl in March greatly reduced killings in the camp. An exceptionally large IS assault on al-Sinaa Prison in January 2022 in SDF-controlled Hasakah that led to seven days of heavy fighting is a stark reminder of the enduring threat the jihadist group poses, but the coalition and SDF response rendered the assault a failure, indicative of the robust cooperation between the two and the SDF’s strong development. Hence, the SDF is a major obstacle for IS activities in al-Hawl and prisons, but the potentially grave consequences of a successful IS breakout operation still make them a point of concern for IS re-conventionalizing.

Finally, IS could find resources for a resurgence outside Iraq and Syria. In 2014, when IS was still accumulating territory, it sent many of its fighters to help establish territories in Libya, which they did successfully. Today, the group’s West Africa Province still controls territory in Nigeria and carries out major military operations against the Nigerian army and the forces of neighboring countries. During the past two years in Mozambique, IS-affiliated fighters seized and then lost the towns of Mocimboa da Praia and Palma. IS-linked jihadists in the Democratic Republic of the Congo staged a complex breakout of 1,300 inmates. Of particular concern is the activity of IS-Khorasan Province (IS-K), the IS affiliate in Afghanistan. One of IS’s more lethal and tactically proficient provinces, IS-K was formed largely by defectors from the Taliban and other jihadist groups and seized territory from the Taliban in 2014–15 before being repulsed by the Taliban and US-backed Afghan security forces. IS-K has benefitted from the US withdrawal, perpetrating dozens of attacks since August 2021, and now wages a fierce insurgency against the Taliban. The growth of IS-K or other provinces could give IS the opportunity to once again transfer experienced fighters to places where it seeks to conventionalize.

Policy Implications

While IS remains in an insurgent posture, we should not forget that its ultimate goal, like that of all jihadists, is to control and govern territory. If given the opportunity, IS is likely to pursue conventionalization again. The organization’s entrenchment in Iraq and Syria in 2013–19 necessitated intensive military efforts to dislodge the jihadists from their territories and led to the deaths of tens of thousands as well as widespread displacement and devastation.

This analysis has identified three flashpoints for a potential IS resurgence: Assad regime territories in the Badia; al-Hawl and prisons under SDF control; and the growth of IS provinces outside of Iraq and Syria, IS-K in particular. Just as US support has been crucial for defeating the caliphate, so too will it remain paramount for continuing effective counter-IS operations in Iraq and Syria. In areas where the United States has lesser or no presence, such as West Africa, Afghanistan, and Assad regime territory, it might exert some pressure through limited airstrikes when needed, but it can also foster its partners’ capabilities so that when the next jihadist conventional campaign begins, we will be prepared to meet it—as we were not in Afghanistan.

Ido Levy is an associate fellow at The Washington Institute for Near East Policy focusing on counterterrorism and military operations, particularly relating to jihadist groups. He is the author of the recently published book Soldiers of End-Times: Assessing the Military Effectiveness of the Islamic State, now available free of charge on The Washington Institute’s website. Free hardcopies are available upon request. You can find him on Twitter @IdoLevy5.

The views expressed are those of the author and do not reflect the official position of the United States Military Academy, Department of the Army, or Department of Defense.