The more serious challenge, for Americans new and old, is to make a common culture that’s greater than the sum of our increasingly diverse parts. It’s not enough for the United States to be a neutral zone where a million little niches of identity might flourish; in order to make our diversity a true asset, Americans need those niches to be able to share a vocabulary. Americans need to be able to have a broad base of common knowledge so that diversity can be most fully activated.