NPR Fresh Air:

On March 15, a 28-year-old Australian man opened fire in two mosques in Christchurch, New Zealand, killing 50 people and injuring dozens more. The shooter had previously declared allegiance to "white identity" — a fact that came as no surprise to J.M. Berger, an author who studies extremist movements.

"We're seeing a resurgence in various countries," he says of white nationalism. "It's a worldwide phenomenon."

Berger, who studies the online activity of extremists, notes that the New Zealand shooter praised President Trump as "as a symbol of renewed white identity" in a 74-page document he published before the massacre. That mention, Berger says, aligns with a trend he found when he studied the hashtags and language used by alt-right Twitter users.

"When we do the social media analysis, it comes shouting out at you," he says. "We can count the links that they put out on Twitter and other social media platforms, and what we find is the most common is '#MAGA.' The most common description of somebody that they use in the profile, they use on Twitter, is 'Trump supporter.'"

Berger is the author of the book Extremism and co-author of Isis: The State of Terror. Listen:

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