Violent extremists march over the bodies of the innocent in an effort to rip societies apart and rebuild them in a darker image.

While extremists do sometimes fight each other directly, they rely on the tool of terrorism to aim their fire at the center of society. The immediate effect is to cut down people who are simply trying to live their lives in peace. The ultimate goal is to destroy the center entirely.

Al-Qaeda’s September 11 attacks aimed to “wake up” the Muslim masses and inspire them to rise up against “corrupt” rulers in the Middle East and the “complicit” West. The Islamic State (ISIS) has advanced this concept into an even more ambitious war to completely eliminate the “gray zone” of peaceful coexistence among sects and religions.

By many meaningful measures, this effort has been a failure. The primary audience for ISIS propaganda and ideology is Muslim. While ISIS has outperformed all of its jihadist predecessors, it has still only succeeded in mobilizing a tiny percentage of Muslims to violence or other direct action.

But terrorism does not simply seek to mobilize supporters. It seeks to mobilize enemies, because the existence of enemies validates its narrative. The extremist’s proposition is that its identity in-group—the nation, race, or religion it seeks to recruit—can never be healthy or safe without taking action against some out-group that threatens it.

Here, too, the Islamic State’s successes have been objectively rare, in terms of absolute numbers. But the growing resonance between ISIS extremism and its anti-Muslim extremist counterparts—most recently embodied in Sunday’s attack on Muslims in London—is creating new risks for escalation. This means not just the possibility that each movement can attract new recruits, but also that their virulent ideologies could seize an ever-larger portion of the public discourse.

In a recent research paper for the International Centre for Counter-Terrorism—The Hague, I explored how identity collectives—such as nation, race, or religion—radicalize into extremism. I found that movements become more extreme when the legitimacy of the in-group, its right to exist as a collective identity, is challenged.

Real violence directed against members of an identity collective is the gravest imaginable challenge to the group’s legitimacy. Extremist ideologies are built from numerous sources, which can include scripture, history, and current events, ultimately boiled down to a collection of selectively chosen facts and outright fictions. Extremists do not require true information to undergird their ideologies, but when true information is available to support their claims, it strengthens their arguments and facilitates an increasingly violent orientation.

The symbiotic relationship between warring extremist groups provides extraordinarily potent grist for that mill. The violence ISIS carries out in the West provides fodder for anti-Muslim extremists, and growing violence against Muslims feeds back into the ISIS narrative. It is likely that this results in improved recruitment of extremist adherents, and it is almost certain that it results in a greater mobilization to violence among those who have already absorbed some portion of an extremist ideology.

When someone is attacked because of their religious, racial, or national identity, they will often question their place in society and the appropriate response. Years of research strongly suggest that extremist groups are particularly attractive to people who feel uncertain about their lives, their identities, and their roles in society.

The destabilizing and unexpected nature of terrorist violence contributes to these feelings of uncertainty, making the adoption of extreme identity-based ideologies attractive to more and more people. When two extremist movements are battling each other using innocent civilians as cannon fodder, the escalating violence and the toxic political rhetoric that follows serves to further amplify that uncertainty. The conflict creates situations that both sides can then incorporate into their own narratives. If the framing of the in-groups and out-groups sync up, the opposing ideologies can fit together like puzzle pieces, each completing the other’s argument about why the out-group is a threat.

Jihadist extremism is a mature extremist movement, fully committed to violence, with a strong center of gravity currently revolving around ISIS, and collection of strong secondary nodes around the affiliates of al-Qaeda and the Syrian jihadist group that recently split from al-Qaeda, Hayat Tahrir al Sham.

Anti-Muslim extremism is currently more diffuse, with a number of different factions and strains around the West and beyond, many of which are embedded in mainstream politics, while others are tacked on to fringe movements; all are gaining ground.

Relatively few major anti-Muslim movements have openly endorsed specific types of violence to date, but that is changing. Anti-Muslim violence appears to be increasing broadly in the post-Brexit, post-Trump era thanks to both ideological and contextual influences. We do not yet know much about the Finsbury Park attacker, and while a witness said he shouted that he wanted to “kill all Muslims,” we do not know whether he was motivated by a clear ideology or by a contagious atmosphere of violence, greatly amplified in our saturated media environment.

The mirror vehicular attacks at London Bridge and Finsbury Park, separated by barely more than two weeks, are only the most striking parallel within a larger social resonance. If the disparate anti-Muslim movements coalesce around a coherent ideology, they are likely to become even more virulent and deadly, adding their own clear stamp to the blood-soaked story that ISIS has written around the globe.

The emerging pattern of reciprocal and escalating violence is a grave threat to free societies, far greater than any threat presented by ISIS alone. If we do not find ways to break the cycle of violence, it will expand, feeding on the very fear and uncertainty it creates, and leading the world into an ever-widening gyre of destruction and instability.