The deadly attacks in London on June 3 highlighted the role of al-Muhajiroun, a militant jihadist network with links to at least two of the three London Bridge attackers: Khuram Butt and Youssef Zaghba. Although the group is relatively unknown beyond the United Kingdom, al-Muhajiroun is one of Europe’s main recruitment gateways for young European jihadists eager to join terrorist groups such as the Islamic State.

In my new book, I write about al-Muhajiroun’s modus operandi to illuminate how contemporary jihadi actors cooperate — a critical aspect of the threat posed by terrorism. In my study, al-Muhajiroun emerges as a paradigmatic example of the growing role that informal actors — such as loose networks and individual terrorist entrepreneurs — play in the collaborative efforts of terrorists to achieve their objectives. This emerging form of terrorist cooperation, which I call networked cooperation, poses unique challenges for counterterrorism.

Cooperation among terrorists is not new, but until recently most examples of terrorist cooperation involved relationships between formal terrorist actors. These include state sponsorship of terrorism, ties between Palestinian groups and left-wing/revolutionary groups, and relationships between jihadi organizations such as those between al-Qaeda and its affiliates.

Nowadays, states and organizations no longer have a monopoly on the planning and production of terrorist violence. A growing diversity of other actors that are capable of effecting transformative change through terrorism have entered the picture in recent years. These actors include a growing number of informal networks and individual terrorist entrepreneurs.

These new actors have not emerged in a vacuum but in an environment increasingly conducive to terrorist collaboration: a formidable and persistent ideology — jihadism — that serves as a key motivator for mutually beneficial cooperation. The Internet, and especially new social media platforms, provide a cheap and effective medium for cooperation. And new and enduring armed conflicts, such as those in Syria and Yemen, offer ample opportunities for militant actors to collaborate on the ground.

The case of al-Muhajiroun exemplifies this trend of networked cooperation. Active in the United Kingdom for about a decade before being officially banned after the London bombings of July 2005, al-Muhajiroun continued to operate in pursuit of its goal to establish an Islamic caliphate. The group reconstituted itself under various names and gained notoriety for, among other things, its staged protests against returning British soldiers.

By 2010, its leader, Anjem Choudary, began operating as a transnational jihadist entrepreneur as he systematically expanded his network outside of Britain. His efforts resulted in the formation of an international jihadist nexus known informally as the Sharia4 movement, named for the Sharia4 prefix used in the names of several of the movement’s participant networks.

Sharia4Belgium — an informal network rather than a formal organization — was the first “franchise” to appear. Choudary not only served as an inspiration to the Belgian network but offered more tangible cooperation that included strategic and operational guidance, financial support and ideological training that he provided via video chat. Within a few years, additional informal networks similar to Sharia4Belgium emerged in Europe and beyond. Many adopted the Sharia4 moniker; others took such names as Straatdawah (Street Dawah), Kaldet til Islam (Call to Islam), or Profetens Ummah (Prophets of the Ummah).

The networks affiliated with the al-Muhajiroun-spawned movement cooperate among several domains, including the ideological, logistical and operational. Before his arrest in 2016, for example, Choudary and some of his British supporters traveled to the Netherlands, where Choudary lectured to members of both Sharia4Holland and Sharia4Belgium about the “methodology to overthrow the regimes.” (Choudary was found guilty of eliciting support for the Islamic State in 2016 and sentenced to prison.) Operational cooperation involved joint protests, demonstrations, and other publicity stunts. Social networking platforms served as the main means to organize these events.

Over time, the al-Muhajiroun network’s links with terrorism became increasingly evident. The movement inspired more than a hundred convicted terrorists, facilitated the movement of foreign fighters to various conflict zones, and cooperated with the Islamic State and al-Qaeda’s Syrian affiliate. Networks affiliated with al-Muhajiroun have encouraged and facilitated their members’ travel to conflict regions such as Syria, Iraq, Mali and Yemen to join insurgent and terrorist organizations active there. Sharia4Belgium, for example, facilitated the movement of Belgian and non-Belgian jihadists to Syria and Iraq, where they became a core component of the Islamic State and participated in a number of atrocities.

Terrorist cooperation is known to boost the capacity and performance of terrorist groups. But as the case of al-Muhajiroun suggests, the challenges posed by networked cooperation are particularly troubling to counterterrorism practitioners. Their networked cooperation involves the collaboration of a diverse type of actors — some of whom have unique operational benefits over traditional organizations.

These informal networks are able to establish ties to other actors more easily and efficiently than traditional organizations, and often under the radar of the authorities. They have greater flexibility and mobility, allowing easier physical diffusion of their participants, which helps the establishment of transnational ties. Informal actors also face fewer barriers for establishing an international presence, and are hence better able to exploit legal loopholes than formal organizations. They can share ideas and information more easily both within and outside of their network, which can advance ideological cooperation and the exertion of ideological influence.

Networked cooperation implies new possibilities of cooperation between organizations and networks; organizations and entrepreneurs; networks and networks; entrepreneurs and networks; and even between sets of entrepreneurs. As the example of al-Muhajiroun shows, these channels of cooperation are not mutually exclusive but can and do coincide to create a highly complex web of multichannel cooperation.

Along these multiple channels, these actors can engage in a plethora of cooperative activities related to terrorism. Coupled with highly enabling environmental factors such as jihadist ideology, the rise of social media, and the prevalence of armed conflict, the overall threat posed by cooperation between contemporary actors has reached new heights in terms of quantity, diversity, and efficiency that no security practitioners can afford to ignore.

Assaf Moghadam is an associate professor and director of the MA program in government at the Interdisciplinary Center Herzliya in Israel; director for academic affairs at the International Institute for Counter-Terrorism (ICT) in Israel; and a nonresident fellow at the Combating Terrorism Center at the U.S. Military Academy in West Point, in N.Y.