The Western Sahel region—a cluster of arid, low-income countries stretching from Senegal, on Africa’s Atlantic coast, inland to Mauritania, Burkina Faso, Mali, Niger, and Chad—is home to the world’s most youthful populations. According to current UN Population Division estimates, about 57 percent of this six-country region’s population is 19 years old or younger. As security conditions deteriorate across the rural Sahel, governments in Europe and North Africa are taking notice of these countries’ demographic status—and for good reasons. Sustained population youthfulness (often called a “youth bulge”) contributes to low levels of educational attainment, joblessness and social immobility, and ultimately to rapid population growth, which tends to drive declines in per-capita availability of freshwater and other critical natural resources: factors that are associated with the risk of persistent violent conflict and represent powerful push factors for migration.

This year, 2018, marks the 60^th anniversary of a landmark publication by a pair of academic social scientists who first recognized the close relationship between population age structure (the distribution of a country’s population, by age) and development. In Population Growth and Development in Low Income Countries (Princeton U. Press, 1958), demographer Ansley Coale (1917-2002) and economist Edgar M. Hoover (1907-1992) theorized that eventual declines in fertility would transform developing-country age structures. Coale and Hoover demonstrated that these newly transformed age structures would exhibit larger shares of citizens in the working ages, and smaller shares of dependent children and seniors (Fig. 1). This transition, they argued, would someday help lift countries with youthful populations in Asia, Latin America, and Africa out of the low-income bracket.

While the World Population Prospects—the UN Population Division’s demographic estimates and projections—will never land on anyone’s non-fiction best-seller list, the latest version holds some noteworthy true stories. And the most remarkable demographic story of all may be Bangladesh’s.

The Kurdish people’s century-long quest for self-determination reveals a key aspect of ethnic separatist conflicts. Ideas of nationhood can endure for generations, unifying people across borders and often making separatist conflicts hard to resolve. But how much harder is it to resolve separatist conflicts than other violent, non-territorial intra-state wars (such as political revolutions)? In practical terms, how much longer, on average, can policymakers expect separatist conflicts to persist and reoccur than the typical political revolution? These are tough questions. Surprisingly, demography helps us find the answers.

After four months of political unrest and more than 250 deaths, the calls for Nicaragua’s embattled president Daniel Ortega to step down are escalating. One of political demography’s most robust statistical findings tells us that countries where an authoritarian government rules a youthful population, any change in regime typically yields an autocracy or at best, a partial democracy. Only very rarely has a liberal democracy emerged immediately after a rebellion in a youthful country (one with a population with a median age under 26 years). Given this, if Ortega is ousted from office, what type of leader should foreign affairs analysts expect to replace him?

Are younger countries at higher risk of civil conflict? The International Crisis Group’s 2018 list of 10 conflicts to watch suggests they might be: Like last year, intra-state conflicts (civil and ethnic conflicts within states, rather than wars between states) dominate the list, and among those, about 70 percent are within youthful countries, or states with a median age of 25.5 years or younger. The only multi-state cluster mentioned in both 2017 and 2018 lists is the Sahel, the world’s most youthful region.

It should be an excellent time to be a young Iranian: High school and college enrollments in the Islamic Republic rank near the top of Muslim-majority countries. Women have only about two children on average, compared to 6.5 in the mid-1980s. And childhood mortality is projected to approach North American levels in the next 15 years. Yet, as the recent protests show, many young Iranians feel left out. Job growth—especially for young adults—has failed to keep pace with development, while persistently high rates of inflation steadily drive up the cost of living and cut deeply into Iranians’ savings.