Countries as "Lego" blocks

I feel a lot of empathy for Branko Milanovic when he writes this (even if not everything he says is an endorsement of my current positions -I would rather have said that the break-up of Yugoslavia was another failure of the arrangements that tried to solve the nationality problem, but of course he knows much more than myself about it):

"I know of many people, myself included, who for several decades had one national identity, and then within months had to start believing they had another one. Anyone who thinks it is a simple process and that people can, at the drop of a hat, start believing the opposite of what they believed for several decades is deluding himself. Anyone who believes that countries are lego-blocks that can be, with ease, put together or broken  apart, is deeply wrong. Just look at the Scottish referendum, Brexit and Catalan strive for independence.

The India-Pakistan Partition in 1947 was and remains a defining moment in the lives of many Indian and Pakistani families, regardless of the fact that it is now almost 70 years old. The break-up of countries (or unification, in the case of Germany) likewise remains a defining moments for many people who had lived through the 1990s in Eastern Europe. Despite my pro-federalist and pro-Yugoslav feelings at the time, I am glad—today—that Yugoslavia no longer exists because I became convinced that managing it would have been impossible. Of all the books on the break-up of Yugoslavia, the most influential for me, was AJP Taylor’s “The Habsburg Monarchy”. It shows the failure of all constitutional arrangements between 1809 and 1914 that tried to solve the famous “nationality problem” in the Empire. Each arrangement solved one problem at the cost of opening another one. Taylor ends the book by pointing out that success or failure of Tito’s Yugoslavia will answer that perennial question of whether it is possible to have a multiethnic federation in Eastern Europe. We know the answer today.   

But the opinion about the inevitability of the break-up that we may hold today, cannot make us forget not only how traumatic and bloody the process was, but also how many of the newly-created countries, from Ukraine to Bosnia, remain utterly fragile and, it seems, permanently suspended over the precipice of yet another war. And how the past extends its long shadow over the present." 
I also read the article by Kuper he mentions. Anti-communist leaders discovered that there are more nationalist than liberal votes, he says. Unfortunately, what is true for the liberals is also true for the social-democrats. I guess some of us try to push for a Europe that slowly becomes more like the Obama's USA than the former Yugoslavia. Perhaps what keeps us hopeful is just a fantasy.  Something else: I can still see the former federalist in much of the work by Milanovic recently and up to today: a paper he has on how a global federalism would look like to improve global transfers, his comment in "The Haves and the Have-nots" that a democratic China would not survive in the absence of a federal system, his comments in the last book about identity politics...