For decades, observers have chalked up Africa’s slow economic growth to corruption, weak institutions, and poor leadership. But these explanations miss a deeper force at work. The single most powerful variable shaping the speed of economic growth, stability, and the chance of democracy taking root across African countries is the age structure of their populations.

A country tends to be most productive when its fertility rate declines enough that working-age adults outnumber children and elderly people in need of care. When young adults make up a large share of the population—and they are educated, in good health, and able to find work—an economy can really take off. Societies whose populations are older also tend to be more democratic and less violent than those with younger ones.

Africa’s fertility rate is still roughly double that of Latin America and South Asia, and the median age in sub-Saharan Africa today is 19.5 years, compared with 29.0 in South Asia, 34.0 in South America, and 43.0 in Europe. But in a few decades, the prime demographic window is expected to open in many African countries: as millions of African citizens mature into working age, the continent’s economic growth could accelerate sharply. Yet the same conditions that can unlock prosperity and democracy can also cause a country to combust if it is governed poorly. If there are not enough jobs to go around, young adults may rise up or be seduced by the promises of strongmen rulers. African countries must thus start preparing today for their moment of opportunity.

In Africa, prospects for prosperity are still largely determined by demography. Currently, the continent is home to 22 low-income and 23 lower-middle-income countries. Because poor countries have limited domestic capital and attract little foreign investment, labor is the primary engine of economic growth. According to analysis using the Pardee Center’s International Futures forecasting platform, growth tends to accelerate when there are at least 1.7 working-age people for each child or elderly person. But today, the continental average is just 1.4 working-age people per dependent.

As countries move into middle-income status, the availability of capital becomes more important than labor for driving manufacturing- and services-led growth. And as countries become even richer, technology and higher-value services, such as finance, steadily become the dominant factor driving economic expansion, overtaking both labor and capital. China, and what are known as the Asian “tiger economies”—Hong Kong, Singapore, South Korea, and Taiwan—all followed a similar pattern: a large working-age population first drove rapid growth, then capital accumulation and technology transfers added fuel to the fire.

Most African countries have not yet benefited from the demographic structure that launched these Asian countries. Africa’s transition was delayed by a uniquely heavy historical burden. The continent’s transition was first slowed relative to other regions because of the removal of working-age people through the slave trade; then, colonial rule left populations poorly educated and disconnected from the infrastructure and institutions needed to participate in the post–World War II surge in trade, industrialization, and technology diffusion. For centuries, Africa’s exceptionally high prevalence of deadly diseases, including malaria and sleeping sickness, also kept mortality higher and population growth slower than in temperate climates, even when women bore seven or more children over a lifetime.

From the 1950s to around 1981, the ratio of working-age people to dependents in Africa was either stuck at low levels or declining, even as these ratios were already trending upward across much of Asia and Latin America. Over the past 45 years, the ratio has slowly started to increase, but it remains below 1.4 across much of the continent. The economic growth Africa achieved from the first years of the 2000s through the mid-2010s was driven to an unusual degree by the high price of oil, copper, and iron ore, itself stemming from China’s industrial expansion and rapid urbanization, not from a favorable age structure.

But Africa’s young population is maturing. The number of African states with a median age above 30 is projected to roughly triple between 2025 and 2050. Fertility has been declining across most........

© Foreign Affairs