Sean Rossman

USA TODAY

The violence that erupted outside the G-20 summit — smashed store fronts, petrol bombs and catapults — marked the latest surge of Black Bloc protests, a European resistance that recently emerged in American political demonstrations.

The Hamburg, Germany, Police Department reported Black Bloc protesters are among the thousands of protesters attempting to disrupt the annual gathering of world leaders. President trump called the protesters, "anarchists."

Black Bloc, is a tactic, not a group. Those who practice it often wear black and cover their face with masks. Typically, they leave a wake of destruction.

In a 2015 article published in Police Magazine, author Kory Flowers said anarchists use protests such as the ones in Ferguson, Missouri, after the shooting death of Michael Brown, to launch their signature "chaos- and havoc-laden tactics." The article described Black Bloc strategy as "throngs of criminal anarchists all dress in black clothing in an effort to appear as a unified assemblage, giving the appearance of solidarity for the particular cause at hand."

Videos and photos of the events in Hamburg show throngs of people dressed in black.

Black Bloc gained attention in the United States in 1999 after violent protests at a meeting of the World Trade Organization in Seattle, according to a 2001 history of the tactic on the anarchist news website, A-Infos. The reason for the dress, wrote the history's author Daniel Dylan Young, was to "fend off police attacks, without being singled out as individuals for arrest and harassment later on."

Hundreds of people were arrested in the Seattle riots, which involved anarchists vandalizing businesses.

Young said Black Blocs spread in Europe in the 1980s as a "popular resistance to the police state and the New World Order." About 3,000 people engaged in a Black Bloc protest in 1987, according to A-Infos, when President Ronald Reagan visited Berlin.

In early February, swarms of people dressed in black invaded what was supposed to be a peaceful demonstration against right-wing commentator Milo Yiannopoulous on the campus of the University of California - Berkeley.

The group tossed smoke bombs, set fires and started fights. Yiannopoulous' speech was canceled as a result. The protest's organizers, the Berkeley Against Trump coalition, said the peaceful acts of the 1,500 demonstrators were marred by 50 to 75 anti-fascist Black Bloc protestors.

Outside of Berkeley, media outlets have linked Black Blocs to a number of modern protests, most recently in efforts opposing President Trump. The Nation credits a Black Bloc protestor with punching alt-right leader Richard Spencer in the face on Trump's inauguration day. The Washington Post said Black Blocs were involved with violent protests in Washington, D.C. on inauguration day and in Portland following Trump's election win.

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