I think our definitions are out of whack. Plus, there is perhaps some nuance lost in the trailer's translation from Japanese. Can you tell me what you mean by "assimilated"?
If you mean in terms of naturalisation, even naturalised Americans of different ethnic groups tellingly identify as both their ethnic descripter and as American (African-American, Chinese-American etc.).
If you mean in terms of cultural assimilation, America is a country of immigrants whose cultures have had a profound impact on predominant American Culture (for example, the US's most famous musical exports, Blues and Jazz, have origins in it's African-American roots).
If you mean linguistic assimilation, then English is the most bastardised language in the world, made up of Latin, German, French and all sorts of other stuff.
These sound more like a kind of cultural symbiosis (AKA multiculturalism) to me, but I'm no anthropologist, so my definition might be way off