The key difference seems to be that patriotism is still a mainstream value in the US. We're much more suspicious of it in Europe. Aside from the racists, hardly anyone in the UK considers themselves patriotic, except in a negative 'At least we're not European' sense.
I'd guess - based on speculation - that France and Germany are mid-way between the two.
Without patriotism there isn't really anything to be assimilated into.
/ After 9/11, Gerhard Schröder declared "We're all Americans now" and I was like "Huh? I'm having enough trouble with being German, thank you." "If you know your enemies and know yourself, you will not be imperiled in a hundred battles." Sun Tzu
