Even within a nation, it is hard to agree on a "national identity".
I guess it depends on the cultural homogeneity in the country. In the UK there is an assumption of homogeneity that breaks down savagely upon close inspection, even before we get into those who arrived in the last couple of centuries.
If we think of millennium old differences then Viking culture left a large imprint upon the north east of England and Scotland. The Celts down the west side of Britain are different again. The anglo-saxons in the south eastern parts of the country. And that's before we figure in the later stuff.
And because these differences are largely ignored, we end up with a vibrant culture but no real idea who the "English" are.
I always imagine that the rituals of belonging in the USA are attempts to create a shared national identity beyond its immigrant cultures. Unfortunately as the the intent is lost in the pomposity of obesiance the ritual becomes pointless. keep to the Fen Causeway
It hardly "breaks down savagely"; of course there are some differences between various areas in England lingering on from the past, and some living in various areas will argue that some cities in those areas, even villages, are very different from each other. However, the question is how significant these are in comparison with differences between England and other nations.
If you go to other countries you tend to suffer from culture-shock, whatever area of the UK you come from, though the severity may differ somewhat. When you meet other English people abroad you become very aware of how much you have in common - despite what might be considered big differences at home.
I recommend "Watching the English" Kate Fox, which I and others find makes us very aware of how very English we are ("Yes I do that/think like that") despite what we thought was our very individual character:
"To a foreign person English are often indecipherable, even when the language is not a firewall. This book is a very good instruction manual of the Englishnes and in addition to that it is absolutely very funny, being nevertheless scientific and correct. All my English friends have been a little bit disappointed to have been revealed so openly." Maybe it's because I'm a Londoner - that I moved to Nice.
