The rise of the alt-right has been one of the defining political movements of the past decade, but comparatively lesser-known is its supposed counter-movement, the alt-left.

Key points: The term alt-left was popularised by Donald Trump after the 2017 rally in Charlottesville

The term alt-left was popularised by Donald Trump after the 2017 rally in Charlottesville Militant far-left groups have gained traction in the US since Mr Trump was elected

Militant far-left groups have gained traction in the US since Mr Trump was elected Experts say far-right movements are more likely to use violence to achieve their aims

The alt-right have been called many things; neo-Nazis, racists, fascist — beliefs which are seen as a departure from mainstream values.

The movement has also been placed under the media spotlight due to the extreme views it expresses in internet forum echo-chambers, and its role in spurring incidents including the Christchurch shootings, which has taken much of the focus away from a discussion of the extreme opposite end of the political spectrum.

US President Donald Trump helped popularise the term alt-left after the 2017 Unite the Right rally in Charlottesville, where he blamed the violence on people on "both sides".

"You had a group on one side that was bad and you had a group on the other side that was very violent and nobody wants to say it, but I will," Mr Trump told reporters.

"What about the alt-left that came charging at the, as you say, the alt-right? Do they have any semblance of guilt?"

Unlike the far right and the alt-right, the far left do not call or associate themselves with the term alt-left.

They do, however, also have a history of violence and the prospect of a militant left actively fighting its ideological opposite is not far removed from history.

The Revolutionary Armed Forces of Colombia (FARC), Shining Path, and the 19th of April Movement were involved in bloody conflicts in South America in the 1970s, while the Red Army faction carried out a series of terrorist attacks in the 1970s and remained active for more than 20 years.

However, whether we will see the resurgence of a militant far left to counter the rising far right remains to be seen.

'The prospect of violence is always lurking'

A 2018 study debunked the theory that the term alt-left is used to describe movements opposing the alt-right. ( AP: Steve Helber )

The term alt-right, an abbreviation of alternative right, is claimed to have been first coined by American white supremacist Richard Spencer.

While the term is ill-defined, it's commonly associated with anti-feminism and a belief in xenophobic, nationalistic politics, including anti-immigration policies.

Mr Spencer is an advocate of the "peaceful ethnic cleansing" of all non-white Americans, but claims he is not a neo-Nazi.

The ABC approached Mr Spencer for comment but he did not respond by publication time.

The term "alt-left" is arguably even more contested, but a study by the European University Institute published in February debunked the theory that the term is used to describe movements opposing the alt-right.

Based on an analysis of social media content and more than a million online forums connected to both sides, the study concluded that the alt-left is an artificial construct by Mr Trump's supporters in an attempt to create an equal counterpart to the alt-right.

Steve Fuller, professor in social epistemology at the University of Warwick in England, told the ABC the term has since been used pejoratively by alt-right members against the Antifa [anti-fascist] movement, particularly through far-right media organisations like Breitbart.

White nationalists are met by a group of counter-protesters in Charlottesville. ( Reuters: Joshua Roberts )

He said while the alt-left have been styled as "social justice warriors" — a characterisation that "captures some visible and vocal members of the left" — it was not fully representative of who they are.

"The alt-right wants the alt-left to appear as socially dysfunctional," he said, adding that the construction of the alt-left is designed to deflect attention from the alt-right's violence.

While the far left is not as prominent as the alt-right, Mr Fuller said it has also sometimes been responsible for aggressive and violent behaviour, especially in the form of censorship including the "no-platforming" campaign — which is seen as a type of "symbolic violence".

"It's worth recalling that the original modern defence of free speech … included the right [for] people to bear arms so [they] can defend themselves against those who violently objected to what they said," he said.

"It's not accidental that whether we're talking about alt-right or alt-left, the prospect of violence is always lurking, because violence has always been implicated in the maintenance of the right to free expression."

'The only obvious answer is violence'

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 53 seconds 53 s A member of far-left group Redneck Revolt explains why the left is willing to use violence. ( ABC News )

Some militant far left groups, such as the Redneck Revolt in the US, have gained traction ever since Mr Trump's election victory.

Dwayne Dixon, a member of the far left group Redneck Revolt, told the ABC's Foreign Correspondent program last year that their numbers were rapidly growing in response to the resurgence of white supremacist groups.

Mr Dixon insisted his decision to bear arms was for self-defence, and because it's his right as a US citizen.

"We want our story told because it's ordinary people standing up against fascism, facing down fear, and attempting to reshape our small corner of the world into a space of egalitarianism and shared efforts for our needs and desires," Mr Dixon said.

The ABC contacted the Redneck Revolt for comment but have not received a response.

The Redneck Revolt had their guns at the Charlottesville clashes, but did not fire them. ( Supplied: Daniel Hosterman )

However Duncan Stuart, a political theorist from the Australian National University, said a contemporary leftist re-emergence to the level of an organised political movement is unlikely.

Mr Stuart said this is mainly because people who are left-leaning have more political representation.

"There is also a much stronger cohesion around the belief system on the right," he said, referring to its ability to mobilise.

Mr Stuart added that while the far left and the far right are both political extremes, their similarities don't extend beyond that.

He said the beliefs of the far left tended to be tied to class and social mobility, which usually doesn't require violence to achieve their goals.

"Whereas on the right, it's about race, it's about sexual orientation," he said.

"For the right, it's about essential characteristics that cannot be changed, and when you're faced with the situation, the only obvious answer is violence or deportation."