Following the shooting in Buffalo, N.Y., focus has been trained on the "Replacement" theory, also known as "White Replacement" theory.

That's because a white man, who killed 10 Black people and injured three others, posted a 180-page document online that promulgated racist conspiracy theories often referred to as the "Great Replacement."

And he allegedly used the conspiratorial idea that minorities were and would be replacing whites as a reason to justify what he did. The FBI is investigating it as a hate crime.

"I want to be clear, for my part, from everything we know, this was a targeted attack, a hate crime, and an act of racially motivated violent extremism," FBI Director Christopher Wray said Monday.