Excerpted from the Environmental Security Program’s new issue brief, What Demographic Trends Mean for U.S. Policy — full brief available on the Stimson Center website.

Population dynamics underpin many of today’s most urgent societal challenges, yet these factors are rarely mentioned in policy discussions. As Cornell University demographer Parfait Eloundou-Enyegue notes, “If there is any century in which we have to think carefully about population, it is this century.” The 21st century is defined by simultaneous demographic shifts as population:  

• grows rapidly in some places while shrinking in others;  

• ages at historic speed in some regions while others remain youthful; and 

• redistributes from rural areas to cities.  

Understanding how these dynamics impact U.S. priorities like healthcare, cost of living, fiscal policy, and national defense is essential for crafting policies and strategies that are effective and resilient in the face of demographic changes.  

Youth bulges: Between 2000 and 2025, fertility rates declined in every UN region. But populations in Sub-Saharan Africa and South Asia remain strikingly young, and by 2050, the number of working age peoples in these regions will grow by more than 1 billion. Already, the number of workers —especially skilled and educated workers — in these regions has risen faster than the net supply of jobs. In India, young people account for 83% of the unemployed; in Indonesia, 16% of young people aged 15-24 are out of work. Projected increases in the youth population represent an enormous potential economic asset for these regions, but only if their countries have the jobs, education systems, and institutions to support them. 

Urbanization: Countries must grapple with shifting policy priorities as shifting demographic trajectories influence urbanization rates, rural-to-urban migration, distribution of urban growth (i.e. growth in medium versus large cities), the informal labor force, and informal settlement growth. Between 2000 and 2020, South and Southeast Asia and Sub-Saharan Africa saw the fastest urban growth compared to other regions, due to both rapid rural-to-urban migration as workers seek economic opportunity and natural increase. Urbanization presents unique challenges and opportunities across the urban continuum from rural areas to small and medium-sized cities to megacities.

Aging in the U.S: The United States is aging. Between 2010 and 2060, the ratio of people who are not of working age (i.e., under 15 and over 64) relative to every 100 people of working age (15 to 64) is projected to nearly double: from 21 to 41 non-working people per 100 working age people, compounding pressures on Social Security and Medicare, which depend directly on the ratio of working-age contributors to older beneficiaries. At the same time, aging is increasing demand for elder care while the caregiver workforce shrinks. For instance, the U.S. has only 7,300 certified geriatricians—far below the estimated need of 30,000 by 2030.

Declining population is particularly acute in rural communities of the U.S. Between July 2024 and June 2025, roughly half of rural U.S. counties lost population, with declines in natural population growth (births minus deaths) driving depopulation in two-thirds of these counties. As a result, rural communities are facing hospital closures, lower federal infrastructure investment, and labor shortages. 

Aging in high-income countries: Population aging is not just a U.S. concern; it’s a challenge for almost all high-income countries, with significant implications for U.S. allies’ military capacity, economic growth, and global stability. Age-related spending pressures are projected to increase in the average OECD country by nearly 6.25% between 2024 and 2060. Countries that are simultaneously aging, fiscally constrained, and whose defense-eligible population is shrinking will face hard choices that affect their capacity to contribute resources to shared security and project stability in their regions. 

Immigration: Immigration is key to offsetting the pressure of aging. As deaths rise and births remain low, net migration to the U.S. can help sustain the workforce and support economic competitiveness. Prior to the second Trump Administration’s enforcement measures, immigration was projected to become the primary driver of U.S. population growth by 2030. Between July 2024 and July 2025, however, immigration added just 1.3 million people to the total U.S. population, down from a peak of 2.7 million between 2023 and 2024.17 With natural population growth remaining steady, and a lower level of international immigration, the total U.S. population grew just 0.5% to 341.8 million in 2025—the slowest growth since 2021, during the COVID-19 pandemic.

Read the full brief here.

Lauren Risi is a Senior Fellow and Director of the Stimson Center’s Environmental Security Program.

Claire Doyle is a Research Analyst in the Stimson Center’s Environmental Security Program.

Madelyn MacMurray is a Research Assistant in the Stimson Center’s Environmental Security Program. 

Sources: International Monetary Fund; Labor Mobility Partnerships; The Institute for Policy, Advocacy, and Governance; Al-Jazeera; World Bank; Nature Cities; U.S. Census Bureau; Congressional Budget Office; Bipartisan Policy Center; NPG Aging; Population Reference Bureau; Vanorman 2025

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