For Rural America, Conservative Radio + Fox News, and then when they finally got Internet (which was much more recent than you would suspect in a lot of these areas) they hopped on FB and found other angry people from Rural America to tell them that minorities in cities they never go to are the real problem.

And eventually they got enough bandwidth to go on Youtube and watch PragerU to really make them feel smart and "the few that understand what is really going on."

So you create a large crowd of a single-demographic, which used to be impossible... because to get that many people in one place required going to a city... and very few cities in the US are monocultural. Even the PNW at least had a large Asian population before they allowed Black people to show up.