On 9 January 2015, 22-year-old Yohan Cohen was shot in the head while trying to protect the child of a customer in the Hyper Cacher supermarket in Eastern Paris. He was one of four Jewish hostages killed by the ISIS-inspired terrorist Amedy Coulibaly, who stormed the small kosher grocery shop armed with two Kalashnikov rifles and two Tokarev pistols.

The weapons Coulibaly used in this attack came from a seemingly unlikely source: an arms dealer who was a member of the extreme-right organization Génération Identitaire in Northern France.

The connection between the jihadist Coulibaly, who had sworn allegiance to ISIS, and the far-right extremist Claude Hermant, who last month was sentenced to seven years in prison for arms trafficking showcases the paradox of extremism: a strangely symbiotic relationship between movements which at first sight appear diametrically opposed to each other.

Open gallery view Abdelhamid Abaaoud, architect of the November 2015 attacks in Paris. the worst atrocity in France since World War Two, holding an ISIS flag Credit: AP

While Claude Hermant was facing trial in France last month, the British government banned two neo-Nazi groups operating under the names Scottish Dawn and NS131. "Train for your blood, train for your soil!" reads the slogan that runs with their propaganda videos.

Those videos featured training camps in the style of ISIS fighter camps. The groups’ catchy propaganda articles were modelled after ISIS’s glossy magazines and sophisticated videos.

As these white supremacists’ attempts to copy Islamist extremists’ recruiting strategies and imitate their modus operandi illustrate, far-right and Islamist extremists have more in common than they like to admit: their tactics cross-inspire one another, but more importantly, their intellectual backbones are strikingly similar.

In 1932, the French biologist Alexis Carrel published his pseudo-scientific bestseller ‘L’homme, cet inconnu’. To many it may come as a surprise that his study of the human nature and arguments for voluntary eugenics inspired both the pro-fascist Vichy Regime in France and Al-Qaida’s foremost ideologue Sayyid Qutb.

Extremists share the same ideological fundaments because their worldviews tell the same story; a story that pits supposedly homogenous cultural or racial entities against one another.

Today’s extremists build on victimhood narratives such as the 'global Muslim oppression by the West' or, conversely, 'the Muslim invasion of the West'. Inherent to both Islamist and far-right extremist world views are anti-Semitic tropes and conspiracy theories that blame inevitably the 'the globalist Jewish elites'.

Open gallery view People stand next to candles and flowers placed on the ground, after a terror attack claimed by ISIS that killed at least 14 people and wounded over 120 in Barcelona, Spain. Aug. 20, 2017 Credit: Emilio Morenatti/AP

Osama Bin Laden’s son, Hamza, stressed the role of Jews and Israel in the ‘global oppression of Muslims’ in his 2015 video message. Meanwhile, Andrew Anglin, the founder of the neo-Nazi website Daily Stormer accused Jews of orchestrating a 'white genocide' by "redefining America from what it was founded as – a white nation – into a nation of immigrants."

Radicalization doesn’t happen overnight; it is a gradual process. The radicalization journey of most of the neo-Nazis I spoke to in the course of my undercover research for my book The Rage: The Vicious Circle of Islamist and Far-Right Extremism started with legitimate concerns about immigration and terrorism. Their fears were exploited by far-right figures who transformed their rational fears of jihadist violence into irrational anxiety of the entire Muslim community, Islamophobia.

This created a window of opportunity for extremist attempts to ‘redpill the normies’ (radicalize normal people) by tailoring their anti-Jewish conspiracy theories to the grievances of vulnerable communities.

"Man drives over pedestrians in London! "Not terrorism" say the Jewish lackey cops!", one comment reads on Gab, a platform commonly used by the extreme right. "Jewish liars now trying to hide the terrorist attacks. Unreal!" writes another user after a car crashed into a crowd of people near London’s Natural History Museum on 7 October 2017.

At the Institute for Strategic Dialogue, we studied the evolution of Islamist and extreme-right narratives, finding that campaigns on both sides often mutate into hatred towards Jewish public figures such as Fed chair Janet Yellen, Goldman Sachs CEO Lloyd Blankfein, and philanthropist investor George Soros, and end up in deeply anti-Semitic echo chambers, where National Socialism is glorified and the Holocaust denied.

Far-right populist politicians play into the hands of both Islamist extremists and neo-Nazi radicalization attempts by alienating Muslims and cultivating a climate of anti-establishment hatred.

Open gallery view Activists from the Egyutt (Together) party tear down an ad by the Hungarian government against George Soros in Budapest. July 12, 2017 Credit: Pablo Gorondi/AP

With provocative slogans such as "Let’s not let Soros have the last laugh" on official posters adorning Hungary’ walls, Prime Minister Victor Orban’s last election campaigns coincided with a wave of anti-Semitic hate crimes in Hungary. Meanwhile, one of Trump’s campaign ads blamed "massive illegal immigration" on "these people that don’t have your good in mind". Despite his pro-Israel policies, occasional winks to conspiracy theorists such as showing the faces of Jewish billionaire investors when alluding to an orchestrated mass immigration provided ammunition to the anti-Semitic extreme right.

Open gallery view The cover of ‘The Rage: The Vicious Circle of Islamist and Far-Right Extremism’. Credit: Julia Ebner

Al Qaeda and the alt-right are cousins, not enemies. Both want to destabilize the world order, both share a virulent anti-Semitism. The cumulative nature of extremism demonstrates that approaches that focus exclusively on one or the other - or come at the expense of the other - are doomed to fail.

The international community should take a more consistent approach to extremism, and counter dehumanizing rhetoric that unites extremist groups on all ends of the political spectrum.

Julia Ebner is a terrorism and extremism researcher, and author of The Rage: The Vicious Circle of Islamist and Far-Right Extremism (2017). She is Research Fellow at the Institute for Strategic Dialogue and Global Fellow at the Project for the Study of the 21st Century. Twitter: @julie_renbe