Authorities say the shooter who killed 22 people and wounded dozens of others in El Paso, Texas, Saturday acted alone. In a narrow sense that may be true, but experts warn that it’s important to recognize his actions were rootedin a wider movement of white nationalism and violent extremism that is behind a growing number of mass murders.

In Christchurch, Munich, Quebec City, Birstall, Pittsburgh, Charlottesville, Oslo and other cities around the world, white supremacists have killed innocent people in calculated acts of hate. Lawmakers and the media oftendescribethesekillers as “lone wolves,” who radicalized in isolation and whose actions were a unique aberration. But each found homes in a sprawling online network of racist propaganda, where fellow extremists offered them a sense of community and purpose. Each attack directly informs and encourages others, creating a decentralized network of violent white supremacists who share similar goals.

“These attacks are symptomatic of basically a very powerful global movement that is just not adequately captured by describing these perpetrators as lone wolf actors,” said Vidhya Ramalingam, founder of Moonshot CVE, which develops counter-extremism programs and software. “Even to consider them simply domestic terror threats would be an underestimation.”

The first sentence of the El Paso shooter’s alleged manifesto proclaimed support for the killer in Christchurch, New Zealand, who killed 51 people in two mosques earlier this year. The Christchurch attack also inspired the anti-Semitic Poway synagogue shooting in California in April. Before their attacks, all three gunmen posted to the hate-filled message board 8chan, where a cheering audience of supporters lauded and critiqued the murders.

But the threads connecting white supremacist attacks stretch past this year’s massacres and predate the online platforms that have accelerated the spread of their ideology. The Christchurch shooter cited Norwegian mass murderer Anders Breivik as inspiration. Breivik, who killed dozens of children at a youth summer camp and bombed the capital of Norway in 2011, found his own inspiration in part on the now-defunct American white supremacist site Stormfront, which was founded by a former grand wizard of the Ku Klux Klan.

The white supremacist movement has for decades encouraged lone attackers as part of a “leaderless resistance” strategy, Ramalingam said, in which extremists operate independently to commit violence and are in turn celebrated and copied by other killers. The result is that rather than a visible terror cell or gang, would-be perpetrators form an amorphous mass that is harder for law enforcement to target.

“It’s not an approach that’s entirely dissimilar from some of the tactics that were adopted by ISIS and other groups,” Ramalingam said.

In ISIS, however, there was a more centralized leadership structure and a common procedure for promoting attacks. An ISIS supporter may never have met with any of the group’s leaders, but they usually made it clear they were acting on behalf of the group.

“In some ways, this was easier with [al Qaeda] and ISIS because individuals acting on their behalf expressed allegiance to the group in noticeable ways,” said Amarnath Amarasingam, a senior research fellow at the Institute for Strategic Dialogue, a counter-extremism think tank. “It’s not always the case with neo-Nazi or white nationalist groups.”

These attackers don’t have a centralized group to pledge allegiance to and don’t always state in plain terms they are acting on behalf of white nationalism, which can lead to speculation from politicians and the media about their motivations. When there is a white supremacy-inspired killing perpetrated by a lone actor, the focus more often turns to the individual’s psychological history, family background and criminal record. Although non-white extremists are rarely granted the same rich biographical details, Ramalingam says these individual stories do offer important context for attackers. But the overemphasis on white supremacists’ backstories also tends to ignore their place in the broader movement.

“It’s quite easy to dismiss them as lone actors with a mental illness or crazy kids playing video games,” Amarasingam said. “We have to start seeing white nationalism as a coherent ideology — with ideologues, with writings and literature, with symbols, with music, with culture — in order to combat it effectively.”

Whenlawmakers focus on mental health or video games, they are also deflecting responsibility from those who have emboldened the white supremacist movement, from President Donald Trump to far-right pundits that traffic in anti-immigrant hysteria. It is easier to blame self-radicalization and mental illness than it is to acknowledge a congressman promoting the same racist conspiracy theory that served as the title of the Christchurch shooter’s manifesto, and that mass killings — like that in El Paso — do not happen in a vacuum.

Accurately addressing white nationalism would require lawmakers to admit that they are sometimes accessories to its growth, as Trump and others within the Republican Party derive much of their support from playing to the worst of white grievance politics. The result is a dynamic that former President Barack Obama called out in a lengthy statement on Monday that appeared to be directly aimed at the president.

“There are indications that the El Paso shooting follows a dangerous trend: troubled individuals who embrace racist ideologies and see themselves obligated to act violently to preserve white supremacy,” Obama said.

“We should soundly reject language coming out of the mouths of any of our leaders that feeds a climate of fear and hatred or normalizes racist sentiments; leaders who demonize those who don’t look like us, or suggest that other people, including immigrants, threaten our way of life, or refer to other people as sub-human, or imply that America belongs to just one certain type of people.”