The "Antifa" movement, which US President Donald Trump officially classified as a "domestic terrorist organization" on Monday, brings together groups claiming to be anti-fascist and generally associated with a fringe of the radical far left.

Antifa or "anti-fascist" is an umbrella term often used by the right wing in connection with violence at protests.

"Antifa is a militarized, anarchist enterprise that explicitly calls for the overthrow of the United States government, law enforcement, and our legal system," according to the executive order signed Monday by Donald Trump.

The White House expressed its intention last week to crack down on what it calls left-wing "domestic terrorism" following the assassination of ultraconservative influencer Charlie Kirk on September 10.

Donald Trump then announced that he wanted to classify the "Antifa" movement as a "terrorist" organization, without explaining the legal consequences of this decision.

The Antifa movement is more akin to a movement than an organized group. Lacking leaders or a formal structure, it instead refers to informal groups operating independently, according to American historian Mark Bray, author of a seminal book on the subject, comparing it to feminism, which inspires numerous movements without constituting one as such.

While acknowledging that the movement posed a public order concern, the former director of the FBI, the American federal police, Chris Wray, estimated in 2020 that it constituted "not a group or an organization, but an ideology."

Its members, often dressed entirely in black, denounce racism, far-right ideas and what they consider fascism, and believe that violent actions are sometimes justified.

The Antifa movement, which originated in Europe, emerged in the United States during Donald Trump's first term, notably after a far-right demonstration in Charlottesville, Virginia, in August 2017. A car struck a group of anti-racist activists who had come to confront the far-right groups. One person was killed and around twenty others were injured.

Following Donald Trump's remarks last week, Hungary's nationalist Prime Minister Viktor Orban, the US president's main European supporter, urged the European Union to emulate the United States, arguing that "this violent far-left network has carried out brutal attacks across Europe, including in Budapest."

In 2020, Donald Trump had already raised the possibility of designating the movement as a "terrorist" organization. The United States was then rocked by sometimes violent protests following the death of George Floyd, an African-American man suffocated by a white police officer in Minneapolis (north).

The United States does not currently have a list of "domestic terrorist organizations."

Tyler Robinson, the alleged murderer of Charlie Kirk, who explained his actions to his loved ones by the "hatred" he said the influencer conveyed, used ammunition engraved with anti-fascist inscriptions.