Generally, in this essay, Anna Quindlen writes about a USA of many different cultures and how they live in the same country and, even despite all differences, can feel like one after such a disaster like the 9/11.
Anna believes that nowadays, immigrants from Mexico and some other countries are seen just like the immigrants from Ireland or Italy were seen back in their days.
In a way, she shows us that this is what the USA has always been. A country of immigrants, of different people, different cultures and different races, but one single nationality.