Editor’s Note: In recent years, so-called homegrown violent extremists (HVEs) have eclipsed returned foreign fighters and other sources of terrorism. National Defense University’s Kim Cragin assesses the HVE threat and finds that, contrary to popular opinion, Western security agencies are disrupting many HVE plots and otherwise doing well against this potentially dangerous threat.

Daniel Byman

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U.S. and European security officials often say that the greatest terrorist threat to their countries comes from homegrown violent extremists (HVEs). Yet the situation is not quite as dire as their statements suggest. Even as the overall number of plots by HVEs sympathetic to the Islamic State have increased in recent years, security officials also have gotten better at disrupting them.

Homegrown violent extremists are individuals who do not travel abroad to fight for a foreign terrorist group but, rather, remain home to conduct attacks. The term refers to individuals sympathetic to the Islamic State or al-Qaeda, as well as right-wing extremists. HVEs often are inspired by propaganda they witness on social media. Some interact virtually with like-minded individuals from around the world through social media, including through encrypted apps.

The seemingly random and spontaneous nature of HVE attacks gives the impression that they are impossible to stop. This has been particularly true for attacks associated with the Islamic State. In July 2016, for example, Mohamed Lahouaiej-Bouhlel drove a truck through a promenade in Nice, France, killing 84 people and injuring more than 300. Lahouaiej-Bouhlel had researched previous terrorist attacks online. He was sympathetic to the Islamic State, but he had no formal ties to this foreign terrorist group.

The sheer number of attacks by HVEs sympathetic to the Islamic State further reinforces this impression. Over the past five years, Islamic State supporters have attempted 455 attacks outside Syria, Iraq or other declared territorial provinces, also referred to as external operations. These numbers include both successful attacks and plots disrupted through law enforcement interventions but not plots halted by military strikes in Syria or Iraq against Islamic State planners. Of these 455 external operations, 363 (80 percent) were executed by Islamic State sympathizers or HVEs (see Figure 1). The remaining 20 percent were conducted either by foreign fighters who have returned home (also known as returnees) or by those who have relocated to another country and pursued terrorist attacks.

Despite the impression that HVE attacks cannot be prevented, security officials regularly stop them. Among more recent examples is the arrest of Rondell Henry in Prince George’s County, Maryland. He allegedly plotted an attack against pedestrians at National Harbor, a popular waterfront district with outdoor entertainment areas. Henry told authorities that he had watched videos of Islamic State fighters on social media for two years and had modeled his operation on the attack in Nice. Henry was discovered via a missing person investigation.

This is not an isolated case. Local security officials—primarily law enforcement—have halted 58 percent of the 363 attempted attacks by HVEs sympathetic to the Islamic State over the past five years. Admittedly, the success rate for disrupting inspired attacks is not as high as for those orchestrated by Islamic State plotters overseas (69 percent). But something is going right. We just need to discover what.

To answer the question of what is going right, it is important to start with an understanding of how HVEs fit within the overall strategy of the Islamic State. When Abu Bakr al-Baghdadi announced the creation of a caliphate in Syria and Iraq in June 2014, Islamic State leaders encouraged Muslims from around the world to immigrate to Islamic State-controlled territory. More than 40,000 people traveled to fight with the Islamic State in Syria and Iraq. Islamic State leaders also pursued external operations. In November 2015, they met near Tabqah to discuss the best way forward to spark attacks in the West. The Islamic State’s campaign against the West eventually took two forms: sending fighters home to orchestrate external operations and encouraging HVEs to conduct attacks on their own.

The Islamic State has used various forms of social media over the past five years to encourage HVEs to execute attacks locally. The most obvious have been speeches by Islamic State leaders, encouraging sympathizers to launch attacks against the West. This continues. In a video titled “March Forth Whether Light or Heavy,” which began circulating online on May 14, Baghdadi tells followers:

“O Muslims! Do not think the war that we are waging is the Islamic State’s war alone. Rather, it is the Muslims’ war altogether. It is the war of every Muslim in every place, and the Islamic State is merely the spearhead in this war. It is but the war of the people of faith against the people of disbelief, so march forth to your war O Muslims. March forth everywhere, for it is an obligation upon every Muslim who is accountable before Allah …. [W]e call upon every Muslim in every place to perform hijrah to the Islamic State or fight in his land wherever that may be.”

This general approach—speeches released on social media platforms—is not unique to the Islamic State. Al-Qaeda leaders also have issued speeches encouraging sympathizers to execute attacks against the West. Yet al-Qaeda has been less successful than the Islamic State in prompting HVEs to act. This suggests that Islamic State propaganda alone is not responsible for the significant number of operations by its sympathizers.

Beyond propaganda, Islamic State virtual planners and recruiters also have used a combination of public-facing and private social media platforms to identify sympathizers, nurture relationships and prompt individuals to act. Foreign fighters have played important, yet highly fluid, roles in this effort. Sometimes they plan the attacks. Sometimes they recruit HVEs. Sometimes they amplify Islamic State propaganda. In December 2018, for example, Germany charged Islamic State member “Jennifer W” with crimes committed in Syria. She had traveled to Syria in mid-2015, joined the Islamic State and then returned home in early 2016. Upon her return to Germany, Jennifer W. orchestrated an online jihadi chatroom to recruit women.

These networks—both virtual and physical—are what distinguish the Islamic State from its predecessors. They allow Islamic State leaders to continue to threaten the West with external operations, even as they lose control over territory in Syria and Iraq. But most of these operations are neither random nor spontaneous. In fact, it is not quite accurate to say that 80 percent of all Islamic State external operations have been executed by HVEs alone, as implied in Figure 1. A significant number of these operations are better characterized as virtually planned or recruited, locally executed. Only 36 percent of Islamic State external operations have been truly inspired, without any known ties to its recruitment networks.

These networks are vulnerable to attack. Military strikes have killed not only battlefield commanders but also Islamic State virtual planners in Syria and Iraq. Law enforcement agencies also have arrested and prosecuted Islamic State recruiters, bloggers and other agitators back home. Based on my research, approximately 190 Islamic State recruitment cells have been dismantled and their members prosecuted since June 2014. An additional 21 virtual planners and 28 media emirs have been killed on the battlefield, according to Operation Inherent Resolve press releases. These types of activities have allowed security officials to mitigate the recruitment of a new generation of foreign fighters and HVEs.

We have found a way to minimize the risk of HVE attacks. It combines traditional investigative techniques—both online and in person—with more aggressive efforts against virtual planners, recruiters and agitators, both home and abroad. This is not to argue that the approach is easy. Significant resources are required to execute this type of campaign consistently, and past solutions do not always translate into future success. But if security officials can continue to disrupt the Islamic State’s virtual and physical recruitment networks, we’re in pretty good shape.

* The data in this post were derived from a database developed and maintained by the author at the National Defense University. Kira McFadden, Dominique Reichenbach and Grace Strelich also contributed to the database. It includes all successful external operations conducted by Islamic State operatives and sympathizers. It also includes all publicly reported disrupted plots, defined as the arrest of perpetrators who have identified the target, purchased the weapons and made plans (e.g., logistics) to conduct the attack. It does not include arrests, for example, for money sent abroad to the Islamic State or attempted travel to Syria. Although not included in these specific numbers, the database also incorporates plots disrupted by the U.S. military and its allies through airstrikes on Islamic State external operations planners in Syria and Iraq. Operation Inherent Resolve regularly provides updates on its strikes and often names the Islamic State operative targeted. If basic research through media reports and/or Islamic State propaganda confirms that these individuals helped plan a previous attack, then this strike is counted as “disrupting” a future plot.