The Missouri man who fatally shot three police officers and wounded three others in Baton Rouge, Louisiana, this week was an adherent of the extremist, conspiratorial and sometimes violently anti-government "sovereign citizen" ideology that's been a factor in other incidents targeting law enforcement and government officials across the South and nation.

The Kansas City Star published court records showing that Gavin Eugene Long, a 29-year-old ex-Marine who served in Iraq, filed paperwork with the Jackson County, Missouri, recorder of deeds in May 2015 to change his name to Cosmo Ausar Setepenra. In a seven-page filing laden with bizarre, pseudo-legal language, he declared himself a member of the "United Washitaw de Dugdahmoundyah Mu'ur Nation."

The group, which claims to be part of a sovereign black indigenous nation within the U.S., is part of a larger, loosely organized sovereign citizens movement that's been gaining adherents in recent years — and raising alarm among law enforcement officials. The Southern Poverty Law Center (SPLC), which monitors sovereign citizens, has estimated their numbers at 300,000, but precise figures are elusive because they typically operate as individuals without established leadership.

Sovereign citizens were the top concern of U.S. law enforcement agencies in a 2014 study by the National Consortium for the Study of Terrorism and Responses to Terrorism, surpassing even Islamist terrorists. The FBI identified sovereigns as a significant domestic terrorist threat back in 2010.

"Not every action taken in the name of the sovereign citizen ideology is a crime," the FBI noted, "but the list of illegal actions committed by these groups, cells, and individuals is extensive (and puts them squarely on our radar)."

The sovereign citizens ideology has roots in the far-right, racist, anti-Semitic Posse Comitatus movement that began in the late 1960s and holds that the sheriff is the highest legitimate law enforcement authority. ("Posse comitatus" is Latin for "power of the county.") The concept of the "sovereign citizen" came from retired U.S. Col. William Potter Gale, who became a Posse Comitatus activist in California and a minister in the white-supremacist Identity Church. Sovereign citizens reject federal, state and municipal law for their own unconventional interpretation of common law.

Some sovereign citizens maintain a white-supremacist ideology. For example, Allen Scarsella, the man who confessed to the shooting of five Black Lives Matter protesters outside police headquarters in Minneapolis last year, was a sovereign citizen who reportedly held intensely negative opinions about African Americans.

But in recent years, SPLC reports, a growing number of black Americans have been attracted to an offshoot of the sovereign ideology that takes the movement's conspiratorial and anti-government elements and blends them with selective teachings of black nationalists. Many of the groups call themselves "Moors" or "Moorish," a concept drawn from the ideas of Noble Drew Ali, a North Carolina native who went on to form the black nationalist Moorish Science Temple of America in the early 1900s; however, that group's leader has disavowed sovereign citizens, telling SPLC that his organization "has been misunderstood by people who see the value of our religion but don't want to conform."

Sovereign citizens have borrowed a strategy pioneered by Posse Comitatus known as "paper terrorism": the filing of false liens and other types of pseudo-legal documents in an effort to harass government officials. In Pinellas County, Florida, for example, one sovereign citizen fought a required $20 dog license with a court battle that dragged on for months and ended with the overwhelmed prosecutor dropping the case. And while typical criminal dockets might have 60 to 70 entries, those involving sovereigns might have as many as 1,200.

Black sovereign citizens have been involved in schemes to move into homes they don't own in states including Georgia and North Carolina, which has been a hotspot for activity by people claiming Moorish ties. Earlier this year, for example, a woman calling herself a Moorish national was convicted of trespassing and other crimes after she falsely claimed ownership of a vacant 5,200-square-foot house in Charlotte, North Carolina. Black sovereigns have also inundated courts with bogus filings and targeted officials who investigate them by filing false liens.

This week's shooting of police officers by Long appears to be the first time a declared sovereign citizen who is black has physically attacked police. However, white sovereign citizens have been involved in numerous violent threats and outright attacks against government officials and law enforcement. For example, Terry Nichols, a conspirator in the deadly 1995 bombing of the federal building in Oklahoma City, was involved in the sovereign citizen movement.

While there have been violent incidents nationwide involving sovereign citizens, many have occurred in the South:

* West Virginia, September 2015: Authorities charged Thomas David Deegan, 39, with threatening to commit a terrorist act by plotting a violent takeover of the state Capitol in Charleston. A self-proclaimed sovereign citizen, Deegan held a series of conference calls telling participants "we are at war" and asking them to take up arms to physically remove government officials from their offices. He also allegedly discussed sending armed supporters to attack law enforcement and National Guard facilities. Deegan was sentenced to two to eight years in prison.

* Florida, February 2015: A man who ambushed Orange County Sheriff deputies in a Publix parking lot claimed to be a sovereign citizen. The incident began when a woman called officers to enforce a domestic injunction against Joseph Paffen, 46; when deputies arrived, he fired at their SUV. Two deputies suffered minor injuries and Paffen was shot and killed.

* Georgia, June 2014: Sovereign citizen Dennis Marx, 48, of Cumming shot Forsyth County Deputy Daniel Rush in the leg in an attempted assault on the local courthouse. Officers shot and killed Marx on the scene. Homemade explosive devices were later found in his home. Marx had been involved in a lawsuit against the sheriff's office, and his filings used the pseudo-legal language that typifies sovereign citizen documents.

* Texas, September 2012: Facing federal tax charges, sovereign citizen Phillip Monroe Ballard, 71 was charged with offering $100,000 in a plot to kill U.S. District Judge John McBryde, who was scheduled to preside over his trial. Ballard was found guilty the following year and sentenced to the maximum 20 years in prison.

* Louisiana, August 2012: People affiliated with the sovereign citizens movement were among a total of seven charged with crimes including murder in the deaths of two St. John the Baptist Parish deputies during a shootout in a trailer park. One of the men involved in that case had landed on the terrorist watch list after a string of criminal incidents in other states.

* Texas, July 2011: Sovereign citizen James Michael Tesi, 49, shot at Colleyville police officer John Fossett in Hurst, Texas; Fossett was not hit but Tesi was shot twice and injured. The incident was the culmination of a series of encounters Tesi had with police over refusing to wear a seatbelt, speeding, failing to show up in court, and driving without a valid license. Tesi was eventually sentenced to 35 years in prison.

* Arkansas, May 2010: Two police officers in West Memphis — Bill Evans, 38, and Brandon Paudert, 39 — were shot and killed when they stopped a father-son team of sovereign citizens during a routine drug interdiction stop on Interstate 40. Two other officers were wounded in the shootout that followed, and the suspects — Jerry Kane Jr. and his 16-year-old son, Joseph, of Ohio — were killed.

* Texas, February 2010: Andrew Joseph Stack III, 53, deliberately crashed his single-engine aircraft into an Austin office building housing an Internal Revenue Service field office, killing himself and IRS manager Vernon Hunter, 68, and injuring 13 other people. Stack is regarded as part of the sovereign citizen movement because of what's been called his "blender salad of legal theories" related to the government and taxation.

* South Carolina, 2003: A dispute over surveying for a road-widening project in Abbeville led to a 14-hour shootout between a family of sovereign citizens — Arthur and Rita Bixby and their son Steven — and officers with the city police department, county sheriff, South Carolina Highway Patrol, state Department of Transportation, and the state Law Enforcement Division. It ended in the deaths of Abbeville County Deputy Sheriff Sgt. Daniel Wilson, 37, and State Constable Donald Ouzts, 61, and the arrests of the Bixbys. Arthur Bixby, who was committed to a mental hospital, and Rita Bixby, who was sentenced to prison for conspiracy, both died in 2011; Steven Bixby remains on death row for murder.

Police have not been the only targets of sovereign citizen violence: Earlier this year, sovereign citizen Erick Shute was arrested for killing three of his neighbors in rural West Virginia following property disputes with the men, who he gunned down ambush-style with an AR-15 as they cleared brush near his property.

And in Plano, Texas, 33-year-old sovereign citizen Anson Chi was badly injured in June 2010 when a bomb he was building to blow up a natural gas pipeline in a residential neighborhood detonated prematurely. Chi, who is Asian-American, was sentenced to 20 years in federal prison for possession of an unregistered firearm and malicious use of an explosive.