The fact that the US has recently become home to an extraordinary number of immigrants also may indicate a new direction for the country as it moves on toward 400 million people, probably sometime in the middle of the century.

"It says that we're going to be a country that is more outwardly reaching to the rest of the world, that we'll be more multicultural than we've been in the recent past," says William Frey, a demographer at the University of Michigan and the Brookings Institution think tank in Washington.