Years of being told that they were second-class citizens, from all vectors. School curriculum for the intelligent people, mass media for everyone else. A culture that incentivizes failure to a certain degree, and actively works against those who try to claw their way out of it. Preferential treatment by colleges and universities, in many cases subsidized, where young, impressionable people can be radicalized. Marxism sounds nice to people who want handouts and historically have been given said handouts. We made progress since the LA Riots, 9/11 happened and people put everything else on the backburner for a while. Then Kanye West made a comment after Hurricane Katrina. It set things back a bit but it was a deliberately inflammatory comment by a person known for being deliberately inflammatory. What truly set race relations back half a century was when the President of the United States said "You know, if I had a son, he'd look like Trayvon," From there it was a matter of time until this grand experiment went from a slow descent into a nosedive. He made that comment in in 2012. Would you really believe someone if they told you that there would be three straight months of rioting because a man who put a gun to a pregnant women's stomach would overdose on fentanyl in police custody?
As for your second point, yes and no. It depends on the day, and how the election goes. Ultimately, the problem isn't going away any time soon. There are misguided white people who believe that they will be allowed to exist unmolested if we maintain our current course because they have the correct opinions. These people are too ignorant or arrogant to learn the lessons of South Africa. They want to divide us by race, because if we came together in a true class war, it would be those same professors, talking heads, and community organizers that would be going to the gulags. The intellectual elite, the coastal liberals, the bloggers, all of them would be taken from their shoebox apartments and sent to labor in the flyover states that they hate so much (but are also fleeing to as their golems grow sentient). We could stop all this overnight, but it keeps people from looking at who really controls the country.
The other option is balkanization, and the mass killings that come with forming new countries. I have met people who lived through the dissolution of Yugoslavia, this is the worst thing that can happen.