The sweeping racial changes transforming the United States come with an important demographic dimension: age. The waves of Hispanics and Asians and multiracial Americans reshaping the country’s population are full of young people, who by some measures already outnumber their white counterparts. The trend was punctuated by the arrival in 2011 of the ﬁrst “majority-minority” birth cohort, the ﬁrst in which the majority of U.S. babies were nonwhite minorities. Consequently, the racial makeup of the nation’s younger population is beginning to contrast sharply with that of baby boomers and seniors.

For most of U.S. history, the white population has been viewed as “mainstream” society, with sociologists viewing the assimilation of immigrants and ethnic minorities as dependent on their adoption of its way of life. Not coincidentally, whites were the numerically dominant racial group in the United States during that same time. (Between 1790 and 1980, whites ranged from 80 to 90 percent of the population.) But whites’ tenure as America’s mainstream population is on the wane, in a demographic sense.

The most recent information from the census and elsewhere shows how quickly the shift is happening. From 2000 to 2010, a decade during which the white population as a whole grew by just 1.2 percent, the number of white children in the United States declined by 4.3 million. Meanwhile the child populations of Hispanics, Asians, and people of two or more races were increasing. In comparative terms, whites constituted just 53 percent of America’s young people (down from nearly 70 percent in 1990) while Hispanics constituted 23 percent (up from just 12 percent). Smaller white populations already are evident in institutions that serve youth, such as elementary and secondary schools, and census projections show the white child population continuing to decline for years to come. White children will become a minority of children under age 18 well before 2020, and, soon thereafter, the white population as a whole is projected to begin to decrease.

For most of the lifetime of today’s young people—nearly one-half of whom already are members of racial minorities—America’s white population will be shrinking.

The reason for the divergence is straightforward: In the white population, there will be fewer births than deaths, and nowhere near enough whites emigrating to the United States to make up the difference. Both of those trends are expected to continue, even as the minority child population will continue to rise, regardless of future immigration scenarios. With white fertility below replacement level, there will not be enough births to keep the total white population from falling. At the same time, there is a growing presence of new minorities among women of childbearing age, a result of the immigration of relatively young adult populations from Latin America and Asia in previous decades. Although minority fertility rates are gradually decreasing overall, the crude birth rate (births per 1,000 persons) among most minority groups remains higher than that for whites.