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A new edition of “Diversity Explosion” by William Frey argues that a multiracial younger generation is a critical addition to the nation’s population, not a replacement.

The U.S. fertility rate has fallen to another record low, according to the latest report from the Centers for Disease Control and Prevention: Continuing a two-decade trend toward fewer children, the general fertility rate for women fell by 1% in 2025. The resulting decline in the U.S. population under 18 has fueled anxious commentary about an aging nation and prompted pro-natalist proposals in Washington.

Demographer William H. Frey argues that this conversation leaves out the most important part of the story. In the newly released third edition of Diversity Explosion, first published in 2015, Frey contends that the country’s growing racial and ethnic diversity is what keeps America from shrinking and aging even faster.

America’s rapidly changing racial demography will shape America to a greater degree than ever before, says Frey, a senior fellow at Brookings Metro and holds a longtime affiliation with the University of Michigan’s Population Studies Center at the Institute for Social Research:

“Racial minorities will power all of the growth in the U.S. labor force as older white baby boomers continue to retire. They will make the difference between growth and decline in small towns, suburbs, and exurbs. And they will alter the nation’s electorate such that neither major political party will be able to afford to ignore the interests of all racial groups.”

America’s growing diversity is not ‘replacement,’ Frey said at a Brookings Institution event marking the book’s release. “It’s an important addition, because otherwise we would be declining in our population. We’d be aging even more rapidly.”

The big picture

Frey’s sweeping analysis draws mostly on U.S. Census Bureau data, and it shows that key 21st-century transformations are already in place. Since 2000, Hispanic, Asian, and multiracial populations have grown rapidly as America’s aging white population declined; migration and economic advances have expanded the Black American middle class and moved Black populations into the suburbs; and, Frey predicts, we are two to three decades from becoming a nation in which no racial group is the majority.

From a demographic perspective, the diversity explosion is occurring ‘just in time,’ says Frey, as new generations are bringing needed manpower and brain power to the workforce and residents for otherwise stagnating housing markets.

Hispanic, Asian, and multi-racial “new minorities” grew fastest from 2000 to 2020. Hispanic Americans are the nation’s largest minority group and are markedly younger than the population at large. Frey notes that most Hispanic population growth today comes from births to people already living in the U.S., not from new immigration. 

The 2020 census captured these population shifts. For the first time, most Americans under age 18 are people of color. Among Americans 75 and older, more than 70% are white. Overall, people who identify as something other than non-Hispanic white made up 42% of the population in 2020, up from 10% to 20% for much of the nation’s history.

Even zero immigration won’t reverse the trend

Frey challenged the idea that cutting immigration would return the country to the demographic profile of the 1950s.

Census Bureau projections to 2040 model four scenarios: high, medium, low, and zero immigration. Population size varies widely across them. High immigration pushes the population to roughly 370 million, while low immigration would shrink it to about 326 million, below today’s level. Frey notes that immigration especially strengthens the working-age population, which matters more as birth rates fall.

On diversity, though, every scenario points the same way. The country was about 58% white at the time of the 2020 Census. Under high immigration, that share would fall to 51% by 2040. With no immigration at all, it still falls to 55%.

“We don’t need to have immigrants to become more diverse,” Frey said. “We’re already fairly diverse in our younger ages, and the children and grandchildren of those folks are going to be growing up.”

Frey projects that the 2030 census will show about 44% of Americans identifying as people of color, and well over half of those under 30.

A “cultural generation gap”

A central theme in Frey’s analysis is the “cultural generation gap” that helps explain why the fertility debate is so charged. 

Older, predominantly white Americans grew up in a much less diverse country, and surveys have repeatedly shown them more uneasy about demographic change. Younger Americans, including young white Americans, are far more comfortable with it.

The gap appears in voting. In 2024, Frey’s data show, voters under 45 favored Kamala Harris while older voters favored Donald Trump. Frey called the shift toward Republicans among Hispanic voters in 2024 “a blip” driven largely by economic discontent. Hispanic voters who said their finances had worsened voted strongly Republican, while those whose situations were the same or better kept voting Democratic.

Signs of integration, and lingering barriers

Frey’s book also documents how the ‘diversity explosion’ is challenging long-standing racial barriers and inequalities in America. Black-white residential segregation remains high– roughly 44% of Black residents would have to move to be distributed the same way as white residents, in Frey’s analysis– but trends that are poised to continue are breaking down ghettoization. 

Black Americans increasingly live in suburbs, and Hispanic and Asian populations have spread well beyond traditional “melting pot” states to about 140 fast-growing “new Hispanic destinations” across the Midwest, South, and Northeast.

Interracial marriages rose from less than half of 1% of marriages in 1960 to about 11% in the 2020 census, and more than 20% of new marriages are interracial. 

Looking toward 2050

Reliable demographic data, much of it from the census, is the foundation for planning everything from school construction to congressional representation. These data tell us who will make up the next generation of workers, students, caregivers, and voters, and where resources are needed for schools, housing, language access, and health services. 

The Trump administration has proposed to stop asking people in the U.S. about their race and ethnicity in the upcoming 2030 census. 

“Without these,” Frey warned, “the country would lose the basic data needed to enforce civil rights and voting rights laws.”

The current “diversity boom” may be as consequential for the 21st century as the baby boom was for the 20th.

Frey expects that by 2050, Americans will look back and judge how the country handled it. As birth rates fall, the nation’s demographic future is already visible in its classrooms, playgrounds, and maternity wards, and it is multiracial.

“Diversity is here for the future,” Frey said. “This is a good news story for America.”

“Diversity Explosion,” out this September in its third edition, is published by Brookings Institution Press.

This post was written by Tevah Platt, communications manager for the University of Michigan Population Studies Center at the Institute for Social Research. The photo, courtesy of the Brookings Institution, is by Paul Morigi.