We've always been a nation of many nations. The culture of New England is different from the culture of the Deep South, which is different from the cultures in the West Coast or the Midwest. People living in the cities have different beliefs than people who live in the countryside. Within those areas, there are ethnic, linguistic, and religious enclaves. It's always kind of been like that (probably to a lesser degree in the past), and somehow we've been able to find enough common ground to keep this country together for more than a century.
However, something has changed. You can feel it in the air. Our nation has clearly never been this divided since the Civil War. A lot of people noticed it after the last election, but the truth is that these divisions have been deepening for decades, and they're just now reaching a very noticeable breaking point. That's obvious enough when you look at how the left and the right have been going at each other. It used to be a war of words, but it's turning into something very dark.