> it might be a case for societies where is a stronger group identification (e.g. identification for the nation)
Did you mean nation as in ethnicity? Because otherwise I think the US's identification with the nation is pretty strong across both camps.
> And again, American political system is rather unique in the Western world.
It is? Even with multiple small parties, you'll still largely get ideological camps. It's rare that you have parties that pick their ideas from all over the place.
> Nation can be seen as an consensus ideology and if you share some opinions you can get along better on other topics.
In some sense, it's the job of public education, particularly through the curricula of history and $local-official-language, to establish that consensus ideology - to create unity by exposing everyone to the same large landscape of stories, opinions and beliefs, so that any two people of a nation can quickly establish some common ground between themselves and get along.
> to create unity by exposing everyone to the same large landscape of stories, opinions and beliefs
Or, in other words: to the same reality (it doesn't matter whether it's factually accurate, only that it's widely shared).
Is there a way back to more shared reality without one side wiping out the other? A common threat that just makes the differences in perception meaningless next to the shared perception of that threat? Aliens invading would probably help, at least temporarily. Maybe, if you keep that up for two generations, they'll have forgotten most of the ideological identities that had divided them, and will only rediscover them after some amount of lasting peace?
Sure, and some political decisions have broad consensus in the US as well, e.g. Medicaid. But that really doesn't say much, because other topics are different and the NHS being broadly accepted doesn't help with collectivism vs individualism, pro/anti-EU etc.
to refer back to my original point: Other nations have a more common ground so the study result might not apply to other countries. I think I showed enough reasonable arguments for that potencial case.
And again, American political system is rather unique in the Western world. At least it should discussed in the discussion chapter.