I know we have talked about nationalism before but I have just read Dominion by CJ Sansom.  It is an alternative history from May 1940, where the government of England decided not to continue with the fight against Germany and instead had reached by 1952 an alliance with Germany.  The book is the struggle between a Resistance movement in Britain and a German/British Secret Service whose methods are a mix of pressure and torture, culminating in forced round-ups of Jews and their sympathisers. 
At the end Sansom talks of the real history, including Churchill’s strengths and weaknesses, his complex character, and the other real people.  His PM during the book was Lord Beaverbrook and in this section he quotes Clement Atlee “who did not say such things lightly” as saying he was the only truly evil person he had ever met.  But Sansom’s real target is nationalism: he is writing near the time of the SNP’s campaign for an independent Scotland and comes across as strongly against this.  And certainly against Brexit (though I don’t think it had that name then - this book was published in 2012). He said "The words National Movement” (used by the Scots) should send a shiver down the spine of anyone who remembers what those words have meant so often in Europe.”  (I personally was quite supportive of Scotland breaking away from the UK, but that's probably just because I was interested to see what would happen next, though that sentence doesn't make much sense when I think how I feel about Brexit.) 
He talks about the school of thought in the 1980s that questioned Churchill’s idea of fighting to the end in WWII.  John Charnley and then Alan Clark argued that it would have been better to have accepted Hitler’s peace offer.  Sansom is arguing very strongly against this, thinking it would have led to the scenario he writes about. 
The sentence I found most interesting, though is this one: “ However, a government which accepted the peace terms in 1940 would inevitably have had to rely more, economically, on the Empire; unrest in India would only have got worse with Britain tied to the Nazis; the breakup of the ‘old’ Commonwealth would have been a distinct possibility.  The New Zealanders, in particular, would have loathed links with the Nazis.” 
Throughout the book, New Zealand was always shown as apart from the happenings in England.  The main Resistance man’s father had gone to New Zealand and was always asking his son and family to join him there.  But why does Sansom think New Zealand in particular would have been so upset? Wouldn't Canada have also been appalled? And other countries? 
Even if you don’t want to read Dominion it would worthwhile reading the last history bit (not part of the novel) for his outline of the people and how dangerous nationalism can be.

I'm no great fan of "alternative histories", thinking the activity of inventing them would be fine if only people bothered to first at least learn the actual history involved. So many of the "alternative" versions are predicated on an imperfect or woefully incomplete understanding of what really happened prior to the point of departure into fantasy, or even when this understanding is pretty good (as I am sure Sansom's is, even if he has that peculiarly English trait of misunderstanding or dismissing ex-colonies' actual geo-political identity and role as largely irrelevant) that it requires quite a bit of dependency on the author's own subjective sociological, philosophical, political and other received views in order to hypothesise after that point. "Real world" observation should be sufficient to dissuade anyone from assuming that an uncontentious view exists, so any averred "fact" within the hypothesis is fundamentally the opposite to that which the study of history attempts to establish as such. The real danger is that people then fail to distinguish between these crucial qualititive differences between fact and fantasy and devalue the former as they invest faith in the latter, and as much faith is placed in "invented history" as "actual history" with little incentive to then attempt to verify the invention against the actual record.

Which is probably what I also think about patriotism and nationalism, two other rather distinct pursuits which would appear to be related but in essence only share a propensity to misapply a sheen of historical factuality to things that never actually happened, or certainly often didn't occur in the manner that the patriot or the nationalist chooses to believe. Patriotism at its core is simply a pride in one's perceived geopolitical place of origin, and is an encumbrance only if this pride blinkers one to the point of limiting one's ability to empathically relate to and appreciate others who may question what it is exactly one sees that justifies such pride. It is seldom dangerous, often irritating, and very much an anathema to objective understanding of history. It is a virtue most evidently, and probably only, when invoked as a political and sentimental communal rallying point of reference when resisting the actions of an aggressor who threatens that identity in very real terms through overt military and political means.

Nationalism on the other hand is something that subverts this supposed virtue of patriotism, along with all its potential for simplistic and selective historical appreciation as well as the very language it adopts, and then attempts to translate it into a whole slew of political, socio-economic and military policies, ranging in motive from an ideology of self-determination as identified by the average patriot to ones involving aggression, expansion, enrichment at the expense of others, and even genocide.

We are currently witnessing a worldwide trend towards overt nationalism - exploiting and even encouraging (often spurious and fantastical) patriotic sentiment as it has always been inclined to do - and to no perceivable ends except those which history teaches us are always the ultimate motive for those who steer and actively lead societies in that direction. It is the age-old manifestation of what occurs when a laudable aspiration of political self-determination is pursued without having first paused to determine what that "self" might actually be in realistic and factually historical terms. Policies informed by nationalistic sentiment predicated on such ill-informed and subverted definitions of self will therefore invariably include, and even encourage, ones designed by individuals all too ready to exploit the lack of definition in order to enrich themselves - in the process acquiring power, influence, and sometimes extremely brutal control over the very people who naively (but patriotically) believed that supporting those people and their policies would bring them closer to this nebulously defined state of self-determination to which they had been encouraged to aspire.