Bilingual countries are inherently politically unstable. Which makes a United States of Europe almost impossible.
Based on what examples?
In much of Europe, the whole idea of linguistic unity is a culturally constructed tradition that reinterprets history backwards. Most European nation states achieved linguistic uniformity only recently and through often draconian means. The British were experts at this, not only at home but also in colonies, which is my Canadian relatives of my father's generation are so resentful about the whole language issue.
The idea that linguistic unity is fundamental to national identity is an idea that was crafted and invented mostly over the last four centuries. And while it now appears to us to be basic to the nature of things, there is no fundamental law of nations that requires that be true.
Let's see, historically we have
- France: truly a multilingual nation until the late 19th century. As of 1800, only 15 of France's 85 departments were majority French speaking. In the 1870s, someone from Paris still couldn't travel to Toulon and understand the conversation in the street. In the 1930s, the central government had to force school teachers to enact corporal punishment against non-French speaking kids in an effort to stamp out local languages. Historian Mona Ozouf recounts how her father, also her teacher, would beat her at school for speaking Breton and beat her at home for speaking French. Check out Eugen Weber, Peasants into Frenchman, for an interesting read on this.
- Britain: I'm not sure when it ceased to be truly multilingual, but certainly the opposition to the introduction of the Book of Common Prayer was based largely on the fact that large numbers of Englishmen didn't speak English at the time
And in present-day Europe
- Belgium... has been bilingual for as long as its been a country, except of course for when it was trilingual and had a Spanish king.
- Switzerland - possibly the most stable country in Europe lo these last 500 years and it's an understatement say it's quad-lingual because really the various forms of Swiss German are perhaps more than dialects (I'm not a linguist, but I know from one end of CH to the other, people can't necessarily converse in their native tongue).
- Ireland - OK, you may have a point there, but the language is a focal point for other tensions, not a source. It's a convenient differentiator. It's a history of oppression at issue there and it would be true regardless of what language the oppressed spoke. Focusing on language in that case is like focusing on skin color in the US.
- Canada - mmm on the surface you have a point, but after a bit of touchiness for a decade or two, they seem to have sorted that out and we don't hear a lot from the Separatistes anymore (and while my father's generation were hot about the issue, my cousins my age not so much)
- The United States - not officially bilingual, of course, but we will probably soon have more native Spanish speakers than Spain (currently about 38 million in the US, if you subtract Basque and Catalan speakers from Spains 47 million, we can't be far off). Tension, yes, but not instability.
- China - OK, there's been some instability there this century, but seen as a whole, a remarkably stable society compared to Europe. In addition to the two languages we think of (Mandarin and Cantonese), there are many other regional languages. Granted, they have the advantage of a common written language, so perhaps it's a special case.
- India - a feast of languages. Every damn state has it's own official language and huge swaths of the country don't speak Hindi. You could argue that India is not a stable country of course and maybe it isn't, but I don't see language driving division in India. Again, it's religion, culture, history. Language is the least of it.
I'm probably missing something obvious, but there is nothing inherent in preventing multilingual geographic units from forming successful federations as far as I can see.
