For much of the period after World War II, most Americans were sure that they’d be in the middle class and that their kids would follow. Strong unions, a slower pace of technological change and only limited globalization meant an average worker, with middle skills, could be middle class. There was something called a “high-wage, middle-skilled job.”

Also, the fact that the Soviets held a nuclear gun to our heads meant we had to stick together to some degree. It made compromise in Washington a necessity, not a luxury, on many issues.

But in the early 2000s, most high-wage, middle-skilled jobs disappeared. Now there is only a high-wage, high-skilled job and a low-wage, low-skilled job. And that has fractured the middle class and left a lot of people behind. The end of the Cold War has meant that no foreign enemy cements us together anymore, save for a brief period after 9/11. And the G.O.P. has lost its way.

That’s why our generation’s civil war is so hard to bring to a truce. There are so many fronts. There’s the battle between those who feel the American dream has slipped from their grasp and those who can easily pass it on to their kids. There’s the one between rural small-town Americans and “globalized” city slickers, who, the small-town folks are sure, look down upon them. There’s the fight between the white working-class Americans who feel that their identities are being lost in an increasingly minority-majority country and the Americans who embrace multiculturalism. And there’s the struggle between men who believe that their gender still confers certain powers and privileges and the women challenging that. There are so many fields of dispute.

And not only have we lost the buffers and cushions we once had, but a generation of leaders has come along, led by Donald Trump, who have made fueling our divisions their business model.

In essence, we’ve moved from “partisanship,” which still allowed for political compromises in the end, “to tribalism,” which does not, explained political scientist Norman Ornstein, co-author, with Thomas Mann, of the book “ It’s Even Wors e Than It Looks: How the American Constitutional System Collided With the New Politics of Extremism.” In a tribal world it’s rule or die, compromise is a sin, enemies must be crushed and power must be held at all costs.

It would be easy to blame both sides equally for this shift, noted Ornstein, but it is just not true. After the end of the Cold War, he said, “tribal politics were introduced by Newt Gingrich when he came to Congress 40 years ago,” and then perfected by Mitch McConnell during the Barack Obama presidency, when McConnell declared his intention to use his G.O.P. Senate caucus to make Obama fail as a strategy for getting Republicans back in power.