Which European countries will most likely fall apart, expand or disappear from the map of Europe in 20-30 years?
Belgium. The going joke is that Belgium is a nation of 5 million Flemish (Dutch speaking) people, 5 million Walloons (French speaking) people, and 1 Belgian - the King. That is not far from the truth. Those two language groups simply hate each other. Having lived there for 6 years I made dozens of observations to support that:
small, bilingual cities (5-10k people) are routinely having two separate systems of fire brigades, because the Flemish brigade would refuse to put out a fire in a French house, and vice versa (never mind that they were all officially Belgian). Not only is this despicable, it is also economically very inefficient and leads to ridiculously high taxes.
there was an accident where two trains were inadvertently set on a collision course. While en route, the driver of one of the trains (a French speaking Belgian) realized what was about to happen, called the control station in panic, asking them to stop both trains and avert a disaster. The staff of the control station was native Flemish. Even though they spoke perfect French, they refused to understand him and did nothing. Rather that listening to a French speaker, and his rather simple message (which they perfectly understood), they preferred to let an accident happen that killed 8 people (see here for the story).
I moved there as a foreigner, speaking very little French, and bought a house in a mixed language environment. I didn't plan it this way, but one of my neighboring families happened to be French speaking, the other Flemish speaking. Initially, the French speaking family was friendly to me, while the other family ignored me. Because of fluent English and German knowledge, I picked up Flemish very quickly, without really studying it. Within 12 months of living there I could give professional presentations in Flemish and subscribed to Flemish newspapers and magazines. The result: now both of my neighbors refused to talk to me, each believing I had declared loyalty to the enemy side. That went on for 5 years.
While I was living there, two Belgian women were doing very well in professional tennis: Kim Clijsters (a Flemish woman) and Justine Henin (a Walloon woman). Tennis is a big sport in Belgium, and Wimbledon is a big event. As long as both of these exceptional athletes were in the annual Wimbledon tournament, as you'd expect, my Flemish friends held for Clijsters, and my Walloon friends held for Henin. However, as soon as one of them was eliminated, they didn't hold for the remaining "Belgian" player. No. Let's say Henin was eliminated from the tournament, and Clijsters remained. As of that point, all my Walloon friends held for whoever (non-Belgian) was playing AGAINST Clijsters, hoping to see her eliminated as quickly as possible.
National political parties are set-up in such a way that you can only vote for parties, and candidates, of your language group. There is a Flemish Socialist party, and a Walloon socialist party. A Flemish conservative party, and a Walloon conservative party, and so on. At birth you are registered for one, and only one, language group, and (once you reach voting age) you are only permitted to vote for parties associated with your language group. You could not, for example, sympathize with a politician from the other language group and vote for her or him.
Since I hold an EU passport, I was permitted to vote in local elections. However, in order to do that I would have had to declare affiliation with one of the language groups, and then been given choices of candidates only from that group. Having friends in both language groups, naturally, I declined to do that.
As a follow-up to the terrorist attacks in Brussels we are now discovering that the various law enforcement organizations (the Brussels region alone has 5 mutually independent police forces - all split along language lines) are ridiculously inefficient, mostly because they are set-up to keep secrets from each other - rather than working together to avoid threats to the country. Not really a surprise.
In Belgium, you are indoctrinated from birth that your tribe (your language group) is your primary affiliation, and everything else (religious belief, political affiliation, etc.) is, at best, of secondary importance. The monarchy really is the only institution that attempts to provide any cohesion for Belgium as a nation. And, frankly speaking, the times when monarchies played much of a significant role in politics are over.
There are lots of things to love about Belgium: the people are excellent (I have many good friends there); the location is strategic; the availability of "Euro jobs" makes for first rate career opportunities; the architecture is second to none; the food superb; the infrastructure is excellent. However, like it or not, this country is headed for splitsville.