FROM THE RISING sales of rap music to the popularity of Spanish-language television, from the mosques and temples that have changed the skylines of many cities and towns to the sea of faces on the streets of New York, Chicago, or Miami—the signs are everywhere that America is the largest multicultural democracy in the world, and it is growing more diverse every day. More than a million immigrants flood into the country each year, bringing with them traditions, languages, cultures, and religions from around the world. As they settle in cities and towns across America and become neighbors, friends, and colleagues of current residents, they change the face of the nation. It is no longer possible to determine who is an American by a person's skin color, ethnicity, or religious beliefs. Even the nation's popular culture—the music people listen to, the fashions they wear...