This is as weird as saying that Chinese Confucian culture means that China will never be able to modernize. Not only is there no clear evidence in favour of it, but there's actual evidence against it. Not to mention, there's been enormous change over the last 120 years in that part of culture. 100 years ago, William Wallace was a Unionist hero for Scots (now he is emphatically a nationalist hero), most people in Canada considered themselves British as did most people in Britain itself (now most people in Britain consider themselves to be English, Scottish, Welsh or Irish first). And even today, at a time when Scotland and Northern Ireland are straining at the bonds of union, the people of Yorkshire, perhaps the most distinctive of the English regions, still aren't very desirous of their own devolved government.
Your argument on Chinese Confucian culture is a good example but I doubt it supports your case. China is about 1/4 of mankind and yet despite its huge size and the enormous pressures in the twentieth century on its society, there was almost no separation movement anywhere of any importance. Almost everyone in China feels that they are part of the nation and that they are Chinese. Taiwan might be the only one of any major importance and the debate is not a product of a separation movement.
Racism of any sort in China is condemned although it does happen. This would be true of most the societies that are Confucian.
As a thought experiment imagine a population of Europe, the Arab countries, Russian commonwealth all considering themselves to be one people, one country. {Please do not take the example too far, I just offer it as a thought].
I would argue that the decline of "Britishness" and the rise of regionalism is the result of the forces that ended the empire and a consequence of the end of empire, not some endogenous cultural propensity to disunity.
Sort of agree, yes it did but even earlier in the early 1900s it was clear that Indians were rejected as were Blacks etc. Even as late as ww2, Australian (whites) were infuriated by the British slurs that they were colonial forces and not equal the British from England.