Alot of it is probably due to the low total fertility rate of developed nations. The white & black population won't grow much over the next 40 years.
http://en.wikipedia.org/wiki/List_of_countries_and_territories_by_fertility_rateA rate higher than 2.1 will (slowly) grow the population. But once a country gets healthcare & a reasonable standard of living, TFR drops to 3.0 or less.
Most of the growth seems to come from immigrants like latinos and asians.
http://www.census.gov/population/www/pop-profile/natproj.htmlThe U.S. population is becoming more diverse by race and Hispanic origin.
The race and Hispanic-origin2 distribution of the U.S. population is projected to become more diverse. As the Black; Asian and Pacific Islander; American Indian, Eskimo, and Aleut; and Hispanic-origin populations increase their proportions of the total population, the non-Hispanic White population proportion would decrease. By the turn of the century, the non-Hispanic White proportion of the population is projected to decrease to less than 72 percent with about 13 percent Black; 11 percent Hispanic origin; 4 percent Asian and Pacific Islander; and less than 1 percent American Indian, Eskimo, and Aleut. By 2050, the proportional shares shift quite dramatically. Less than 53 percent would be non-Hispanic White; 16 percent would be Black; 23 percent would be Hispanic origin; 10 percent would be Asian and Pacific Islander; and about 1 percent would be American Indian, Eskimo, and Aleut.
Non-Hispanic Whites, the slowest growing group, are likely to contribute less and less to the total population growth in this country. Although non-Hispanic Whites make up almost 75 percent of the total population, they would contribute only 35 percent of the total population growth between 1990 and 2000. This percentage of growth would decrease to 23 percent between 2000 and 2010, and 14 percent from 2010 to 2030. The non-Hispanic White population would contribute nothing to population growth after 2030 because it would be declining in size.
According to the middle-series projection, the Black population would increase almost 5 million by 2000, almost 10 million by 2010, and over 20 million by 2030. The Black population would double its present size to 62 million by 2050.
The fastest growing race groups will continue to be the Asian and Pacific Islander population with annual growth rates that may exceed 4 percent during the 1990's. By the turn of the century, the Asian and Pacific Islander population would expand to over 12 million, double its current size by 2010, triple by 2020, and increase to more than 5 times its current size, to 41 million by 2050.