America is a nation of immigrants, but it was always a country that valued and emphasized assimilation. Into the Sixties most Americans de-emphasized their ethnic backgrounds--even Americanizing their last names to avoid being labeled Italian, Irish, Jewish, etc. Look at Hollywood movies from the beginnings into the Sixties--all the actors and actresses used "all-American" names.

The civil rights movement in the Sixties started the trend toward identifying, and emphasizing, national and/or ethnic origin, and taking pride in it. Started with blacks, then became a national trend.