Sorry that I've worded much of this so badly and probably offended half (or more) of the members here. Everything over here has to be so politically correct these days and I'm just too old to have learned "the right" way to talk about things like this. I apologize in advance to everyone. Definitely no smiley there, I'm truly sorry that I haven't put this better.
I'm just an ignorant American but I've always found the EU to be a curious concept. The idea of all of Europe being a complete, true union always seemed like something that sounds like a nice ideal but in practice something that would be impossible or at least very difficult to actually achieve.
In comparison, the US is a very young country and, while there are certainly some regional variations, is fairly homogeneous. Sure there's always been immigrants - except for the relatively small remaining native population who immigrated MUCH earlier than Europeans - but after a few generations, they generally melt into the general "type" (that's a bad word choice but I don't know what would be better but hopefully you get the idea), adding a bit of their own particular "spice" to the mix. (Gosh what a run on sentence!)
Europe, on the other hand, is very old with some very strong regional identities. Those regions have a long, long history of not always being friendly with one another. Heck, they've had centuries of warring with one another. The last century had some of the most brutal and divisive conflicts. I honestly don't understand how some of the countries manage to be even civil with one another. How can the French like the Germans, for example, after the 20th Century? My father lived under German occupation and even after all this time has no intention of forgiving or forgetting after his sister was raped and killed. That's one person's experience of one conflict. There's millions of individuals with similar experiences in Europe, some with generations of such experiences.
There are countries with strong, vibrant and resilient economies (England and Germany for example) and others that are, to be generous, are broken (Greece, Spain, Portugal, Italy). The strong ones getting taxed to support the broken with the broken sometimes seeming to not do anything to improve as long as the strong continue to bail them out. I would think that would be a source of strong resentment.
Conflicts and economies aside, the countries of Europe have just had centuries to develop strong national identities, sometimes quite different from even their next door neighbor. How could anyone realistically expect them to all come together into one, big, happy family? Even in a few decades, it seems like an unreasonable expectation. Throw in religion and the turmoils from the recent immigrants (from this side it sometimes looks like invaders) from the Middle East and I don't see how ANYbody gets along over there.
I know that is grossly simplified and I certainly don't understand all of the issues at all but it always seemed to me that it was naive to expect something like this to work - especially so soon after WWI & WWII.
I don't know, like I said, I'm just an ignorant American from a young upstart and sometimes pretty arrogant country

It's probably me that is naive.