Hatred of those who aren't White, basically. Stridence and division. A belief that they are "superior" for some reason. Preoccupation with racial identity, instead of American identity.
Actually, it's not particularly interesting. Fringe, racially-obsessed extremism isn't interesting to me.
Richard Spencer and his ilk are just as ignorant as the Black Panthers, the BLM and their ilk.
President Trump's supporters have nothing to do with "white nationalism", period. Anyone who tries to claim such an association is a lying sack of sh-t.
What's "interesting" to me is good old fashioned, unifying American nationalism...
It seems to me what they hate is reverse discrimination and white guilt.
Your ascribing antifa and BLM motives to them. I.e. they seem to be more "pro white" whereas the KKK is as much anti black as it is pro white. Antifa and BLM are anti white.
https://altright.com/2017/08/11/what-it-means-to-be-alt-right/
I'm still waiting to see where they've actually done something comparable to a KKK action. For now, all I've heard is talk, which is constitutionally protected by the way.
Though I can't say I'm a big fan of this group, the hysterics over them reminds me of the events leading to Ruby Ridge.