Huge population growth and food insecurity count among the factors that fuelled the revolution in Egypt and serve as a caution for other countries facing human and environmental overload, say analysts.
Egypt -- and Tunisia, Algeria and Yemen to a lesser extent -- found itself in a perfect storm in which massive youth unemployment conjoined with hunger and resentment over poverty to threaten an authoritarian regime, they say.
In just 25 years, Egypt's population has risen by nearly two-thirds, from 50 million in 1985 to around 83 million today, with an average age of 24.
"The demographic change is very significant," said Jeffrey Sachs, director of the Earth Institute at Columbia University, New York.
The rise placed heavier burdens on housing and food production in a country that is mostly desert and depends almost entirely on a river that is in worrying decline, he said.
It also helped created a sea of angry, jobless young people when expatriate work in the Gulf dried up after the 2008 economic crisis.
And it made the world's No. 1 wheat importer more exposed to dissent when global food prices surged to a record high in January. After events in Tunisia, the rise fanned protest which developed into a challenge that toppled Hosni Mubarak.
"It's perfectly understandable how this spark went off, although it's not simple to predict when it's going to happen," Sachs said in an interview.
He added: "This is a global ecological phenomenon, of rising world populations, increasing climate unsustainability and pushing up against the barriers of food productivity in many places."
Youssef Courbage of France's National Institute for Demographic Studies said Egypt's tens of millions of births in the 1980s and 1990s had heightened many of its problems in 2011.
"When a population grows too swiftly, resources per habitant fall proportionately," Courbage said.
This was especially so in the labour market, where "the revolt of youth" stemmed in part from the impossibility of finding a decent job, even with a university education.
Demographic growth in Egypt was around 2.8 percent in the mid-1980s, falling gradually to around 1.8 percent last year, according to US and UN data.
Plenty of other countries are vulnerable to unrest, especially as climate change bites, say some commentators.
Risks of conflict and instability "are especially high" in Africa, South and Central Asia and the Middle East, the US National Intelligence Council said last September in a roundup of expert opinion called Global Governance 2025: At a Critical Juncture.
"My rule of thumb is the dry lands are the most combustible part of the world," said Sachs, who pointed to "all of the Sahel to the Horn of Africa, across the Red Sea to Yemen, Iran, Iraq, Afghanistan, Pakistan.
"This is all one vast ecological zone of extraordinary stress, with a lot of war in it already."
Lester Brown, president of the Earth Policy Institute, a US thinktank, said that "all but a few" of the top 20 countries on the list of failing states had populations growing at between two and four percent a year.
"Many governments are suffering from demographic fatigue, unable to cope with the steady shrinkage in cropland and freshwater supply per person or to build schools fast enough for the swelling ranks of children," he said last week in a newsletter.
In contrast, Richard Cincotta, a US demographer who contributed to the National Intelligence Council report, downplayed these factors as a driver of uprisings.
He argued that nations with a "youth bulge" in their demographic chart face a higher risk of unrest -- and the outcome too is determined by the population's age profile.
"Countries with very youthful age structures have an elevated likelihood of experiencing a civil conflict," he said in an email.
"When the age structure matures -- when the bulge moves into the ages of the later 20s and 30s -- the probability of becoming a liberal democracy becomes more likely."
Cincotta noted that the average age in Tunisia was 29, compared to 24 in Egypt, and this difference in maturity could be critical.
"Right now, Tunisia is nearly at a 50-50 chance (and) Egypt at about 70-30 for liberal democracy," he predicted.
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