If we all want to get along well enough to succeed, we need to be under threat. Not just any threat — We need a common threat.
Consider for example the US Congress. Back in the good old days when I was growing up (70’s and 80’s), they got along pretty well. Not well enough to avoid yelling at each other, mind you, but well enough to compromise on just about everything that required passage (“required” as in ‘the nation will fail if we don’t do this’.) Of course, they had a good reason: if we didn’t keep up the appearance of strength, the Soviets would blow us to smithereens. Several times over, in fact.
There’s nothing like mutually assured destruction to focus the mind. It makes it much easier for a congressperson to say to him- or herself “I may not like this solution, but if I can’t find a way to get along with the other side, we’ll be exposing a vulnerability in our clearly superior democratic, capitalist system.”
Nowadays, we (and in particular, our government) aren’t under a common threat, so there’s no incentive to compromise. And until we are, the political gridlock and partisan warfare will continue to be the norm in Washington.