The Failure of Centralized Governments
Centralized governments have mostly all fallen apart sooner or later. Whether the European Union has a centralized government in Brussels or not is a contentious issue, which is in the eye of the beholder. Whoever wants to see it as a helpful helmsman steering the EU in the best direction cannot be convinced that it is a centralized institution wishing to strengthen its control over its various members. Whoever sees it as a centralized, dogmatic institution that wants to pry into every area of its citizens lives will not be convinced that it is trying to help each of its member states to become more stable and prosperous. And then there are the people who see both sides of the story and see truth in both views.
The one thing that is obvious, however, is that whenever an institution for away tries to tell you what's good for you, you will oftentimes rebel if for no other reason then to spite the one trying to control you. This is the same with countries as it is with individuals. People naturally rebel against the instructions or expectations of parents, schools, teams and societal norms in general even if it does them harm, so it should not be surprising that countries and regions also feel more pride when they reject the tenants of others. Just as there are sometimes tensions between US states and the federal government, there are tensions between a player and his coach.
In Europe these tensions have naturally always had a sharper edge simply because of the diverse histories, cultures, world views, languages, religions and economies of its peoples. Just because the European Union has a monetary union does not mean they can have a fiscal union. Monetary union simply implies having the same currency, but a fiscal union would mean having the same attitude towards money, work, free time, saving etc. Southern Europeans are known to be more relaxed in general, and this is also true in how they handle money and work, whereas northern Europeans tend to be more careful with their money and take their professions more "seriously". Now, one is not better than the other. The tensions come when the European Union government in Brussels tries to define the "correct" policy in economy or politics for all the member states. Naturally, the ideals and customs of the strongest member usually prevails (Germany). This then is why others with different mentalities cannot simply agree right away to a way of thinking that is alien to them. Thousands of years of inbred customs, traditions and views cannot simply be modified or in many cases drastically changed simply because Brussels wishes it to be.
The European Union has become to disparate to handle. Even though many member states appreciate the benefits of union, most are not willing to give up their identities and control to those in Brussels who "don't understand" how things are run in their own countries. There is always a disconnect when a centralized body tries to tell peripheral areas how to run their affairs, and this is only natural. National governments always seem to lose face when they give in to demands coming from foreigners. Just because you are a European doesn't mean that you agree with the ideas coming from other Europeans. The differences in mentality between two neighboring countries in Europe much deeper than the differences between any two states in the United States, making comparisons between the European Union and the United States pointless and misleading.
Let's be honest, no one really feels more pride in being a Minnesotan than being an American, whereas an average German or a Pole or a Bulgarian definitely feels more national pride than European pride in general.
Centralization is always doomed to failure, especially when a center tries to incorporate many very different ways of thinking into one unified thought process.