One major cause is the polarization of news sources (24 hour cable news), this has been going on for 20 years and has been exacerbated in the last 5-10 with social media and algorithms to feed confirmation bias and radical thought and conspiracy.
If groups of people can't agree on the basic facts around an issue, there is no chance for common ground and compromise.
The disaffected are rising up and I do believe this is related to economic status and lack of opportunity. Something needs to change, we need a unifying common sense leadership that is above the political fray. We obviously don't have that with Trump, will we get it with Biden? We'll see, I hope so.