The online call to arms was urgent: “Armed Citizens” were needed to protect Kenosha.

“Law enforcement is outnumbered and our Mayor has failed,” a new group calling itself the Kenosha Guard wrote, summoning gunmen to confront racial justice protesters in Wisconsin. “Take up arms and lets defend our CITY!”

Thousands of people liked the social media message. And the guns showed up.

Civilians carrying assault rifles and hand guns were visible on the streets in Kenosha throughout the chaotic events Tuesday night and into the next morning that left two people dead and another wounded. This included the alleged shooter — later identified by police as Kyle Rittenhouse, 17, of Antioch, Ill. — who was captured on video running with an assault rifle near a Kenosha gas station at the center of the unrest.

Militia-style groups and their sympathizers have become a regular fixture in the United States this summer, appearing at dozens of events and confronting racial justice protesters. Experts who track militia activity have been warning that the proliferation of powerful weapons in untrained hands during tense protests is a recipe for bloodshed.

“When you have all these elements present — a fraught political moment, a lot of misinformation and heavily armed groups — it’s just a question of time until something really dangerous happens,” said Lindsay Schubiner, program director at the Western States Center, which tracks militias and other extremist groups.

The Kenosha Guard, which called on people to bring guns to Tuesday’s protest, denied on Wednesday that it had any connection to Rittenhouse.

Kevin Mathewson, a leader of the Kenosha Guard who helped organize Tuesday’s activity, said in an interview that he had never met or communicated with Rittenhouse. Mathewson, 36, is a former Kenosha alderman now working as a private investigator and security contractor. He said his aim was to “alert the public that there will be other citizens out there willing to protect our lives and property since the police were outnumbered every night.”

Mathewson, who was carrying a pistol and an AR-15, waved away concerns that the armed presence had exacerbated the unrest, saying he was intent on protecting businesses and the residential units above them.

“I happen to agree with what the protesters are saying, but I don’t like seeing my neighborhood burnt to the ground,” he said, adding that law enforcement on the scene had a “positive” reaction to the citizen mobilization. “They were handing out water to some of us, thanking us and greeting us very warmly.”

Video circulating on social media appeared to confirm his account of officers thanking armed civilians and giving them water.

Guns were visible throughout the protest on Tuesday night. Some White men who moved around in military-style formations were carrying assault rifles and wore tactical gear. Others wore the insignia of the “boogaloo boys” — sometimes rendered “boogaloo bois” — a fringe anti-government movement whose members sometimes wear Hawaiian shirts and expect a second American civil war. Some people protesting the shooting of Jacob Blake, a 29-year-old Black man who was shot in the back by police on Sunday, also carried guns.

Rittenhouse, who was arrested and charged with first-degree intentional homicide, was a member of a cadet program for the Antioch Fire Department, according to a department newsletter. He also had posted photos of himself with assault rifles on his Facebook page, as well as messages supporting the police.

Oren Segal, the vice president of the Center on Extremism at the Anti-Defamation League, said a preliminary review of Rittenhouse’s background found no ties to established extremist or formal militia groups. Segal said Rittenhouse’s social media posts showed he embraced the pro-police “Blue Lives Matter” political doctrine. “But there was no indication he had any connection to any extremist movements,” Segal said.

Still, Segal said, Rittenhouse represents a troubling trend of people using their support for the police to justify showing up at protests or riots.

These “self-styled vigilantes” often organize online, based around a loose joint belief that they are needed to help police, Segal said, “but there is no single coherent ideology that is necessarily linking them.”

While some militia groups have decades of history, other militia-style groups have formed recently — or added waves of new members — in response to government restrictions during the coronavirus pandemic and during the protests across the country over police violence this summer.

Their appearances have followed a now-familiar pattern. Often, there is a call to arms spread over social media, sometimes in response to Internet rumors or hoaxes that anti-fascist protesters were planning to loot or damage their communities. Then predominantly White and male civilians have convened at dozens of Black Lives Matter protests, lurking on the periphery, wearing military-style clothes, and carrying assault rifles and handguns.

In recent months, militia-style groups have stormed the Michigan Capitol and rushed to the battlefield in Gettysburg, Pa., following an Internet hoax. Members of these groups say their presence is intended to maintain order and support local law enforcement. Protesters see them as a dangerous and intimidating presence with a racist message. Some of these armed civilians wear white-supremacist insignia and in some cases openly espouse neo-Nazi views against Black people and immigrants.

There have already been shootings during other clashes between protesters and armed groups. One person was shot and critically injured in Albuquerque in June during a clash between a group called the New Mexico Civil Guard and protesters. The local district attorney filed suit after the shooting, attempting to stop the group from assembling and assuming law enforcement duties.

Andy Berg, a member of the Kenosha County Board of Supervisors, said that although he doesn’t support looting or property damage, the Kenosha Guard is “agitating the situation.”

“If they wanted to be law enforcement, they should have put their application in and gone through the hiring process,” he said.

One man carrying a handgun who appeared to be with the Kenosha Guard identified himself on Tuesday night as Joe, a 29-year-old Marine Corps veteran. He said that there were 3,000 people in the group “armed and ready” and that police weren’t defending the city.

“Ain’t nothing being done,” he said. “We’re the only ones.”

The sheriff of Kenosha County, David Beth, said on Wednesday that he thought Rittenhouse was a member of a militia group but he wasn’t sure. Beth told a news conference that he had been asked by a member of the community to deputize a citizen militia to help maintain order.

“I’m like, oh, hell no,” Beth said. The violence overnight was “was probably the perfect reason why I wouldn’t. . . . Part of the problem with this group is they create confrontation.”

Facebook early Wednesday removed the Kenosha Guard page, as well as the personal profile for Mathewson, the former alderman, for violating the company’s policies on militia organizations — part of broader rules about “dangerous individuals and organizations.” Mathewson, who was an administrator of the guard’s page, will not get his profile back, according to a Facebook official, who discussed these details on the condition of anonymity because of the threat of violence surrounding them. A page maintained by Mathewson, as a former public figure, remains active, with nearly 5,000 followers.

Facebook also designated Tuesday night’s shooting a “violating event,” meaning content and accounts found to be associated with it — including the suspected gunman’s — are being deleted. Facebook personnel were in contact with local and federal law enforcement about ongoing events in Kenosha, the official added.

In Wisconsin, adults are allowed to openly carry guns and don’t need a permit or a license for handguns, rifles and other guns, according to the National Rifle Association.

On Monday night, a group of young White men with assault rifles had gathered at Civic Center Park in Kenosha. One of the apparent leaders of the group gave his name only as Luke and described himself as “libertarian antifa.” He said their intention was to “protect” protesters.

“We’re seen as an alt-right thing,” said Luke, who did not appear to be affiliated with the Kenosha Guard. “We’re a lot like antifa, but we’re not centralized. We’re a Libertarian antifa.”

Next to him, a man with a gun wore a “boogaloo” patch and gave his Instagram handle, “johnnytheredneck,” which describes him by saying: “Now all I post about is hating all government.”

About 9 p.m. Tuesday, a reporter for The Washington Post witnessed these men marching into the protest area near Civic Center Park in formation. “We’re not trying to harm anybody,” Luke said Tuesday night. “If the cops are not going to stop them throwing pipe bombs on innocent civilians, somebody has to.”

In an Instagram post on Wednesday, Luke denied that the shooter was part of his group and “didn’t appear to be with any other group.”

“There was a brawl at the gas station, my group got out,” he wrote. “We heard the shooting from our staging location about a mile and a half northwest of the incident. Within 5 minutes of us hearing the shots we were inundated with calls and texts about the shooting. We don’t know who this guy is and I don’t have information about the circumstances of the shooting.”

Luke added in another post that it was time for his “bois” to “withdraw from Kenosha completely.”

Tim Craig contributed to this report.