OVER THE next few decades, the developed countries will age and weaken. Meanwhile, dramatic demographic trends in developing nations-from resurgent youth booms in the Muslim world to premature aging in China and population implosion in Russia-will give rise to dangerous new security threats. Some argue that global demographic trends are progressively pushing the world toward greater peace and prosperity. They are wrong. The risks of both chaotic state collapse and neoauthoritarian reaction are rising.

Everyone knows that the developed world is aging rapidly. Graying workforces will become less flexible, less mobile and less innovative; rates of savings and investment will decline; current-account balances will turn negative and foreign indebtedness will grow. Rising pension and health-care costs will place intense pressure on government budgets, crowding out spending on defense and international affairs; militaries will face growing manpower shortages.

Although it is less widely appreciated, the developing world is also aging. Like the developed world before it, the developing world is now in the midst of what demographers call the "demographic transition"-the shift from high mortality and high fertility to low mortality and low fertility that all societies undergo in the course of development. Since 1970, the average fertility rate in the developing world has fallen from 5.1 to 2.9. Meanwhile, the median age of the developing world has risen from 20 in 1970 to 26 in 2005. It is projected to keep rising to 31 in 2030 and 35 in 2050-at which point the typical developing country will be about as old as the United States is today.

While most experts conclude that the geopolitical implications of aging in the developed world will be negative, a growing school of thought says that the same trend in the developing world will be positive-so positive, in fact, that it will make up for the developed world's growing weakness. It won't matter if the developed countries can't fight a war, because demographic trends will render the rest of the world increasingly pacific.

This argument is based on the well-established relationship between youthful age structures and violent conflict. Throughout history, people have observed that young men are responsible for most of the world's mayhem. Since the mid-1990s, a large body of research has confirmed the close statistical correlation between the likelihood of conflict, especially civil strife, and the size of a society's "youth bulge," which is typically defined as the ratio of youth aged 15 to 24 to the entire adult population aged 15 and over. In the early post-cold-war years, this research triggered alarm among Pentagon planners about how sizable youth bulges in much of the developing world posed significant threats to U.S. interests. But more recently, experts have begun pointing to the projected decline in youth bulges as a cause for optimism. With each passing decade, they say, the propensity of the typical developing country to engage in violence can be expected to decline.

We have dubbed this argument the "demographic peace" thesis. In its most-basic form, it holds that the demographic transition, by bringing about an older age structure, will, wherever and whenever it occurs, also bring social and political stability-and ultimately democracy-in its wake; today's security threats, from terrorism to nuclear proliferation, are just one last speed bump on the road to a more-peaceful future.

Although the demographic-peace thesis may seem plausible, we believe that it is deeply flawed. The demographic-peace thesis fails to take into account the huge variation in the timing and pace of the demographic transition, which is leaving some of the developing world's poorest and least-stable countries with large and lingering youth bulges, even as it threatens to subject some of the most-successful countries to the stresses of premature aging. It tends to focus exclusively on the threat of state failure, as in the Somalia model, while ignoring the threat of neoauthoritarian-state success, seen in the China or Russia model, which is more likely to occur in societies where the transition is already well under way.

More fundamentally, the demographic-peace thesis lacks any realistic sense of historical process. Rapid demographic change, when coupled with rapid development, can itself become a highly destabilizing force. As the developing world's demographic transition unfolds, it is deracinating traditional communities, overturning established economic and social relationships and cultural norms, and fueling a rising tide of ethnic strife and religious extremism. This hardly portends a new era of international peace. It is possible (though by no means assured) that the global security environment that emerges after the demographic transition has run its course will be safer than today's. It is very unlikely, however, that the transition will make the security environment progressively safer along the way.

 

LET'S BEGIN with the transition's very uneven progress. Averages can be misleading. Although it is true that the developing world as a whole is gradually aging, some of the poorest and least-stable nations are not aging at all. In sub-Saharan Africa, burdened by the world's highest fertility rates and ravaged by AIDS (which decimates the ranks of older adults), the average youth bulge is now 36 percent, more than twice the developed-world average. That share will remain practically unchanged over the next twenty-five years. The transition has also failed to gain traction in parts of the Muslim world, including Afghanistan, Iraq, the Palestinian territories, Somalia, Sudan and Yemen. Here fertility rates still tower in the 4-7 range-and youth bulges will linger at or near sub-Saharan African levels for decades to come. Most of these countries have amply demonstrated the correlation between extreme youth and violence in recent decades. If the correlation endures, chronic unrest could persist in much of sub-Saharan Africa and parts of the Muslim world through at least the 2030s.

Meanwhile, many of the developing world's most-rapidly modernizing nations are undergoing the full population shift from young and growing to old and declining at a breathtaking pace-far more rapidly than any of today's developed countries did. The adherents of the demographic-peace thesis apparently do not consider this to be a problem. But in fact, demographic transitions that proceed too fast or too far may turn out to be just as dangerous as stalled transitions.

Take China. With its sudden introduction of a one-child policy in the 1970s, China is now aging rapidly and faces a massive age wave that will arrive in the 2020s just as it is becoming a middle-income country. China has been "peacefully rising" while demographic trends have reinforced economic growth. But by the 2020s, the social and economic stresses triggered by its premature aging will be weakening the two pillars of the current regime's legitimacy: social stability and rapidly rising living standards.

Russia, another country undergoing an extreme demographic transition, must cope with a rate of population decline that literally has no historical precedent absent pandemic. By midcentury, its population will contract by one-third, dropping beneath 100 million. This would constitute a spectacular slide in Russia's world population ranking, from fourth place in 1950 to twentieth place in 2050. When a nation feels imperiled, it may reach for illiberal solutions-and when its geopolitical ambitions are threatened, it may act unpredictably. Russia's demographic future certainly does not square well with its geopolitical ambitions, and its leaders know it. While still president, Prime Minister Vladimir Putin, citing the nation's future economic and security needs, flatly declared Russia's birth dearth to be "the most-acute problem facing our nation today."

 

THE MAJORITY of developing countries-in the rest of the Muslim world, in South Asia and in Latin America-lie somewhere in the middle. Their demographic transitions are neither stalled nor extreme. Their youth bulges are now declining rapidly, as the demographic-peace thesis predicts, while their future age waves are relatively small and lie far over the horizon. Yet here too, the transition is fraught with danger.

To begin with, the transition's impact in these regions is nonlinear. Many countries where youth bulges are now declining will experience a temporary resurgence in the number of young people in the 2020s. Demographers are familiar with this kind of "echo boom": it is an aftershock of the demographic transition. When rapid population growth is followed by a sudden population bust, it causes a ripple effect, with a gradually fading cycle of echo booms and busts that recurs every twenty to twenty-five years. A bust generation is now coming of age in much of Latin America, South Asia and the Muslim world. But by the 2020s, a large echo-boom generation will follow. As it does, the rate of growth in youth populations, which is now slowing in all of these regions, will suddenly reverse direction.

The echo booms of the 2020s will be largest in precisely those countries where fertility has fallen the fastest over the past twenty to twenty-five years and where youth bulges are therefore receding the most rapidly-that is, in precisely those countries where the demographic-peace thesis predicts that the impact of demographic trends will be the most positive. In Iran, whose fertility rate has plunged from 6.6 to 2.1 since 1980, the number of youth in the volatile 15-24 age bracket is due to contract by 34 percent between 2005 and 2020. But between 2020 and 2030, the number will once again surge by 30 percent. Many other Muslim-majority countries, from Libya to Pakistan, will also experience huge, regime-rocking oscillations in their youth populations.

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