Two deadly shootings at the end of 2017 reinforced how the well-worn path from hate speech to action leads certain individuals to resort to lethal violence.

In Reston, Virginia, a teenager who allegedly absorbed neo-Nazi ideology online has been charged with shooting and killing his girlfriend’s parents in a tragic double homicide. The young man allegedly committed the murders after learning that the parents had convinced their daughter to break up with him because of his purported racist views.

There were warning signs: On Twitter, the teenager allegedly retweeted messages praising Hitler, posted derogatory remarks about Jews, and called for a “white revolution.” He is also believed to have mowed a 40-foot swastika into the grass at a local park, The Washington Post reported.

This horrific attack came barely a week after a 21-year-old man in New Mexico who, The Daily Beast reported, frequented white-supremacist websites went on a shooting rampage at a local high school, murdering two students before taking his own life.

While it is impossible to draw a direct line of causation between these brutal acts and the many public displays of white supremacy that took place around the country in 2017, it’s critical not to underestimate the effect of an increasingly visible alt-right and white-supremacist community on people who are already predisposed to racism.

The “Unite the Right” rally in Charlottesville last August was a watershed moment for the white-supremacist movement. The event clearly demonstrated the ability of a fringe movement to captivate the nation’s attention with vitriol and deadly violence. The racist gathering turned the debate over the removal of Confederate monuments into a confrontation—and sparked a national conversation about racism that will continue well past 2018.

That event itself also inspired lethal violence: A participant at the rally allegedly drove his car into a crowd of counter-protesters, killing activist Heather Heyer and injuring nearly a dozen people.

But Charlottesville was just one marker of a larger, problematic trend: From the distribution of white-supremacist propaganda on campuses, to dozens of rallies and demonstrations, white-supremacist activism was visible across the country in 2017, signaling a new willingness by racist groups to put themselves front and center on the American public stage.

A closer look at white-supremacist beliefs helps to shed light on why this upsurge is happening.

Modern white-supremacist ideology is founded on the belief that white people are on the verge of extinction, thanks to a “rising tide” of non-white populations (supposedly controlled by a Jewish conspiracy). As a result, some white supremacists and other racists justify their actions as attempts to “save” their race. When they say the white race is being threatened with “genocide” or “extinction,” it becomes easier for them to justify or rationalize violence in the name of “preserving” the race.