On March 15, 2019, alleged gunman Brenton Tarrant attacked the Al Noor and Linwood mosques in Christchurch, killing 51 and wounding dozens of others. It was the worst terrorist attack in New Zealand’s history. Tarrant is now facing life in prison while New Zealand is re-examining its counterterrorism laws.

Earlier this month, threats were reported against the Al Noor mosque and an image circulated of an unidentified individual wearing a balaclava outside the mosque. The anniversary of the attack is rightfully raising concerns about copycats. Unfortunately, the ideology to which Tarrant subscribed encourages just that. Tarrant’s manifesto, entitled “The Great Replacement,” postulated that the white European identity is directly threatened by invading migrants who seek to replace the prevalent culture with their own. He called this a “crisis of mass immigration … that, if not combated, will ultimately result in the complete racial and cultural replacement of the European people.” Though Tarrant is an Australian who resided in New Zealand, his ideology is built around the concept of a transnational European—i.e., white—ethnic identity.

The Great Replacement concept was popularized by French writer Renaud Camus in his 2012 book, Le Grand Remplacement—“The Great Replacement.” Camus postulated that black and brown immigrants were reverse-colonizing native “white” Europeans. He broke the theory down in a 2017 interview with the New Yorker: “You have one people, and in the space of a generation you have a different people.” Followers of Camus’s theory believe that white Europeans are facing an extinction-level threat from mass immigrations.

This belief has attracted followers across Europe and the United States. During the Unite the Right rally in August 2017, white nationalists marched through Charlottesville, Virginia, chanting, “You will not replace us!” In Europe, the French group Les Identitaires and its youth wing, Generation Identity (GI), warn of the replacement of the native European culture. GI and Les Identitaires seek to counter the Great Replacement through demonstrations and activities such as blocking migrant ships traveling to Europe while warning of “the process by which the indigenous European population is replaced by non-European migrants.”

In the United States, the American Identity Movement (AIM) portrays itself as a patriotic American organization that seeks to protect the American cultural identity “against mass immigration and the scourge of globalism.” The group’s language specifically promotes American nationalism and references ideas such as “the preservation of America’s historical demographics in the face of mass immigration” and protecting “American industry and workers, rather than benefit globalist interests.” AIM was born out of the group Identity Evropa, which was one of the organizers of the Charlottesville rally. Though AIM has since sought to distance itself from Charlottesville, its rhetoric remains firmly rooted in the language of the Great Replacement theory.

And therein lies the danger of professedly non-violent groups like AIM and GI. Tarrant wrote that he could no longer sit on the sidelines and watch the destruction of the European race. If these groups truly believe they are facing an extinction-level replacement, individual members may also decide that demonstrations aren’t enough to save the race and direct action must be taken. On August 3, 2019, Patrick Crusius killed 21 people at a Wal-Mart in El Paso, Texas. Crusius did not belong to these groups but he subscribed to the Great Replacement theory, writing in his manifesto that he supported the Christchurch shooter and warning of a white genocide.

On the anniversary of the horrific Christchurch attack, we must be wary not just of violent copycats but also of the base ideology that informed the attack. AIM and GI continue to stage demonstrations and attract new followers through the Internet. Facebook, Twitter, and YouTube have suspended AIM’s main accounts but many of GI’s social media accounts remain. Both groups continue to maintain active web presences elsewhere. To honor the victims of Christchurch, we must loudly reject the ideology that informed the attack and deny any harbor to those who continue to embrace it.