MOUNT OLIVE, N.C. >> Standing in the North Carolina woods, Chris Arthur warned about a coming civil war. Videos he posted on YouTube bore titles such as “The End of America or the Next Revolutionary War.” In his telling, the U.S. was in chaos and there would be only one way to survive: kill or be killed.

Arthur was posting during a surge of far-right extremism in the years leading up to the Jan. 6 attack on the U.S. Capitol. He wrote warcraft training manuals to help others organize their own militias. And he offered sessions at his farm in Mount Olive, North Carolina, that taught how to kidnap and attack public officials, use snipers and explosives and design a “fatal funnel” booby trap to inflict mass casualties.

While he continued to post publicly, military and law enforcement ignored more than a dozen warnings phoned in by Arthur’s wife’s ex-husband about Arthur’s increasingly violent rhetoric and calls for the murder of police officers. This failure by the Guard, FBI and others to act allowed Arthur to continue to manufacture and store explosives around young children and train another extremist who would attack police officers in New York state and lead them on a wild, two-hour chase and gun battle.

Arthur isn’t an anomaly. He is among more than 480 people with a military background accused of ideologically driven extremist crimes from 2017 through 2023, including the more than 230 arrested in connection with the Jan. 6 insurrection.

At the same time, while the pace at which the overall population has been radicalizing increased in recent years, people with military backgrounds have been radicalizing at a faster rate. Their plots were more likely to involve weapons training or firearms than plots that didn’t include someone with a military background, according to an Associated Press analysis of domestic terrorism data obtained exclusively by the AP. This held true whether or not the plots were executed.

While the number of people involved remains small, the participation of active military and veterans gave extremist plots more potential for mass injury or death, according to data collected and analyzed by the National Consortium for the Study of Terrorism and Responses to Terrorism, or START, at the University of Maryland. START researchers found that more than 80% of extremists with military backgrounds identified with far-right, anti-government or supremacist ideologies, with the rest split among far-left, jihadist or other motivations.

In the shadow of the Jan. 6 attack on the Capitol — led in part by veterans — and a closely contested presidential election, law enforcement officials have said the threat from domestic violent extremists is one of the most persistent and pressing terror threats to the United States. However, despite the increasing participation in extremist activity by those with military experience, there is still no force-wide system to track it. And the AP learned that Defense Department researchers developed a promising approach to detect and monitor extremism that the Pentagon has chosen not to use.

As part of its investigation, the AP vetted and added to the data and analyses provided by START, and collected thousands of pages of records and hours of audio and video recordings through public records requests.

Service members and veterans who radicalize make up a tiny fraction of a percentage point of the millions and millions who have honorably served their country.

However, when people with military backgrounds “radicalize, they tend to radicalize to the point of mass violence,” said START’s Michael Jensen, who leads the team that has spent years compiling and vetting the dataset.