Cynthia Miller-Idriss is professor of education and sociology at American University, where she directs the Polarization and Extremism Research and Innovation Lab (PERIL). Her most recent book, “Hate in the Homeland: The New Global Far Right,” is forthcoming from Princeton University Press.

The shooting rampage that took the lives of 10 people in the German city of Hanau on Wednesday had all the hallmarks of a lone actor attack.

Early analyses of the manifestos and statements left behind by the alleged perpetrator — a white, middle-aged German man — pointed to a combustive mix of racist and xenophobic ideologies, wild conspiracies and paranoid delusions about surveillance, Satan, organized child abuse and more. Observers quickly began describing the shooter as mentally ill.

He may well be. But the more we write off terrorists who are motivated by far-right ideologies as “crazy,” the more we are at risk of glossing over the complexity of how people are radicalized.

White men who commit mass shootings and extremist attacks are more likely to be described as mentally ill compared with other terrorists, whose extremism is typically seen as purely ideologically motivated. Far too often, the implication is that mental illness is the reason for their radicalization and violence.

Radicalization happens when an individual comes to accept an ideology that positions “us” against “them” in a war to the end ...

This is a critical mistake. Mental illness is just one of many vulnerabilities that can drive people to extremist actions — not its cause.

Radicalization happens when an individual comes to accept an ideology that positions “us” against “them” in a war to the end, embraces violence as the moral solution to an imagined existential threat and calls on individuals to join the righteous fight to restore some collective good — whether that is the Caliphate, the nation, white heritage, European-ness, or Western civilization.

A mental condition can make people more vulnerable to this kind of rhetoric and increase the appeal of violent solutions to perceived threats.

In this sense, the alleged German shooter is a textbook case.

In his written manifesto, he expressed paranoid beliefs about secret agencies’ ability to “latch onto” his thoughts and monitor him. He also waxed poetic about the German people and the beauty and superiority of his country, which he described in nationalistic terms, as suffering from “destructive” and criminal racial groups and cultures. He reached the conclusion that these non-German population groups should not exist, and laid out a plan for mass racial and ethnic genocide that would fully eliminate entire national and ethnic groups across more than two dozen predominantly Middle Eastern countries.

But vulnerability to extremist rhetoric does not automatically lead to radicalization. Millions of people suffer childhood traumas, isolation, or mental illness, and do not become radicalized.

For someone like the Hanau attacker to become radicalized, there has to be intense exposure to radical ideological statements that dehumanize the "other," legitimize violence, and call on righteous and loyal supporters to take action that leads to radicalization.

Repeated encounters with language describing Mexican rapists, immigrant infestations or global conspiracies of Jews orchestrating multicultural societies at the expense of white ones affect vulnerable people differently than everyone else.

When paired with language that valorizes and celebrates violence, positions entire groups of people as an existential threat, and calls supporters to take action, violence becomes not only a logical step for radicalized individuals, but a perceived heroic one.

As long as people are consistently exposed to extremist rhetoric, we will likely continue to see extremist violence. This is true whether that exposure is in fringe internet forums or in the campaign speeches of mainstream politicians.

Radicalization relies on mental illness in the same way that it exploits other vulnerabilities

That's why rhetoric matters. In Germany, where support for the far-right Alternative for Germany has grown significantly in recent elections, and where tens of thousands of ordinary German citizens have regularly marched in the streets to protest the so-called “Islamification” of Europe, the frequency with which ordinary citizens encounter anti-immigrant, nationalistic sentiment has grown tremendously.

Violent attacks and plots are increasing too. Last summer, a far-right extremist murdered a German politician he deemed too pro-migration — the first political assassination in Germany since the Nazi era. And just last week, authorities made a dozen arrests in coordinated raids across multiple German states, interrupting an organized terrorist cell that had been plotting mass violent attacks against Muslims.

Radicalization relies on mental illness in the same way that it exploits other vulnerabilities — so that individuals will make the leap from rational to irrational action.

But mental illness is not the cause. Framing it in this way only makes it harder to hold accountable those who peddle the rhetoric that radicalizes.