There is not a single European country whose cultural identity has not been warped due to a cultural melting pot at some point in their nation's history (mostly thanks to the greeks and romans). What most people define as a single 'culture' is already a mixture of several other cultures (English is the most obvious example).

tl;dr there's no such thing as a 'German' or a 'Spaniard' in the sense that most people identify with.

Yes, none of these countries may be as culturally diverse as the US, but I never said they were.