I personally think this is simply a result of how much harder the media is pushing that divide (for all of their various purposes). I actually spent some time last year researching this, because I thought I might have just become an old man thinking how great things used to be. I started reading old news stories fairly randomly, from the present time all the way back to the Vietnam era (and a few rabbit holes to earlier times). The first thing that surprised me was the amount of link rot that exists. I always knew intellectually that it was a problem, but wow. It's bad. The second thing that I found was that indeed, the media hammers on the "us-versus-them" political divide of American politics much, much harder nowadays than even ten years ago. I think Fox News was really the turning point. It opened the flood gates. I always remember thinking how "extreme" Fox News was, but I challenge anyone to look up a few of their older stories from the middle of the last decade. It's child's play compared to what pretty much every media outlet is doing today. You can hardly read a recent news story from just about anywhere without being told how it's supposed to fit into our political worldview, and how we should feel about it, and why it's good/bad/stupid/amazing/"terrifying". And so of course, because of this, people are just responding to the programming. Creating the world they're led to believe we they live in. I think it really is that straightforward.
Did you just look at print? Talk radio has been hammering this since the late eighties. Hell you can probably draw a line straight from the "Moral Majority" shit in the seventies, to where we find ourselves now. I suspect this has always been a big part of American culture, but it's being magnified now either by new tech or malicious actors or both.
Ah, I apologize, I didn't keep notes or save links or anything of the sort, and I keep kicking myself for it. I'm usually pretty good about taking notes just out of my regular habit of doing research, but it was so casual, and I didn't think it would end up taking as much of my time as it did. It's a pretty easy formula to replicate, though. I picked current events that I could remember -- intervention in Kosovo, Bill Clinton's sex scandal, Berlin Wall, first election of Putin, Enron scandal, those kinds of things -- and just started looking up stories, and asked my parents and older friends to help me with events I wasn't old enough to remember before the 80s. I made sure to hit a "good" cross-section of the media outlets of the day.
I'd love to see the Bush/Gore 2000 election play out on social media. I was only a kid but the news coverage seemed pretty mild compared to how I imagine it would be if that happened in 2016.
