BIRMINGHAM, Ala. (AP) — Donald Trump’s choice of far-right publishing executive Steve Bannon as a top White House adviser is bringing new scrutiny to a troubling, decades-old ideology: white nationalism.

The movement generally advocates formation of a nation set aside for whites. Some adherents openly supported Trump for president, and white nationalists have praised Trump’s appointment of Bannon as a senior adviser. Bannon previously headed the Breitbart website that appealed to the so-called “alt-right” — a movement often associated with far right efforts to preserve “white identity,” oppose multiculturalism and defend “Western values.”

White nationalists often support the idea that white people are under attack in the U.S., and need protection from the growth of minority and immigrant groups. Adherents sometimes use the hashtag #whitegenocide on social media to promote their belief that the future of the white race is in peril. They see diversity as a threat to fight, not a goal to embrace.

Here are some questions and answers about white nationalism in the United States:

HOW DID THIS GET STARTED?

Groups including the Ku Klux Klan, which is 150 years old, have espoused various white nationalist ideas. The start of the current white nationalist movement is pegged to more recent years.

J.M. Berger, an author and expert on extremism at George Washington University’s Program on Extremism, wrote earlier this year that many of today’s white nationalists were inspired by “The Turner Diaries,” a racist novel published in 1978. In the book, physicist-turned-writer William Luther Pierce describes a dystopian America in which white people are disarmed by minorities.

Timothy McVeigh had pages from the book with him when he bombed the Alfred P. Murrah federal building in Oklahoma City in 1995, killing 168 people.

IS STEVE BANNON A WHITE NATIONALIST?

Bannon hasn’t commented publicly since being tapped for the White House position, but his former colleagues at breitbart.com dispute any links to white nationalism.

In a statement released to The Hill, a political newspaper published in the nation’s capital, breitbart.com said it had been under intense scrutiny over Bannon’s involvement with Trump and was preparing a lawsuit over media depictions of it as a “white nationalist website.”

The statement added: “Breitbart News rejects racism in all its varied and ugly forms. Always has, always will.”