The arrest of a U.S. soldier with far-right sympathies suspected of plotting an attack on American soil to spark "chaos" has highlighted a challenge for the Pentagon: purging its ranks of extremists.

Jarrett Smith, a private in the U.S. Army based at Fort Riley in Kansas, was arrested and charged in federal court with one count of distributing information related to explosives after offering a detailed explanation to an undercover FBI agent. Smith also expressed interest in targeting members of the leftist group Antifa and heading to Ukraine to fight with a far-right paramilitary group, the FBI says.

But he is hardly the first U.S. soldier to reveal far-right or ultra-nationalist leanings, and some fear the U.S. military is being used as a training ground by extremist groups. The links between the far-right and the U.S. armed forces first came to light in the 1980s when Vietnam veteran Louis Beam came home, joined the Ku Klux Klan and had links to the Order, an underground neo-Nazi group that called for the overthrow of the U.S. government.

Earlier this year, a U.S. Coast Guard officer who espoused white supremacist views, Christopher Paul Hasson, was arrested on firearms and drug charges outside Washington. Hasson, an avowed admirer of Norwegian right-wing extremist Anders Breivik, whose attacks in 2011 left 77 people dead, allegedly had drafted a hit list of Democratic politicians and prominent media figures. Prosecutors have said Hasson identified himself as a "white nationalist for over 30 years and advocated for ‘focused violence' in order to establish a white homeland." And in May, the U.S. Army said it was investigating a 22-year-old soldier over suspected ties to neo-Nazi group Atomwaffen Division.

Even if the U.S. military is seen as the most ethnically diverse institution in the country, it remains a fertile breeding ground for far-right sympathizers. According to a poll conducted among 829 service members in October 2018 by the Military Times, 22% said they had seen signs of white supremacism or racism within the military in the previous year.

The number is similar to one found the year before, shortly after an American neo-Nazi rammed his car into a crowd protesting white supremacists and other hate groups marching in Charlottesville, Virginia in August 2017. In 2017 and 2018, the the New America Foundation revealed that violence from the far-right claimed more victims in the U.S. than attacks by foreign terror groups. A New York Times article published on Aug. 5 drew parallels between the rise of Daesh and white nationalist terrorism, citing similarities between the two violent groups. In 2016, the center claimed that white supremacists have been responsible for more deaths in the U.S. than foreign terror organizations, including Daesh and al-Qaida, after 9/11, citing several examples such as the Wisconsin Sikh temple shooting in 2012. Attacks such as the San Bernardino shooting or the Boston Marathon in 2013 also received a lot of public attention. The Charleston Church massacre, the chilling slaughter of nine black church members by a white supremacist named Dylann Roof in 2016, was one of the biggest examples of rising hate crimes in the country.