The rebellion of youth is not the whole story behind the current upheaval in the Arab world, but it's a big part of it.

"If our society and many European societies are becoming more elderly, it's the reverse in Arab countries," says Brian Katulis, a senior fellow at the Center for American Progress.

The presence of a lot of young people in a country can sometimes lead to conflict. The frustrations of youth who may be repressed or economically dissatisfied have played out in a variety of eras and places, from the French Revolution to the French banlieues - the Parisian suburbs that have seen occasional riots in recent years.

During the 1990s, countries where people aged 15 to 29 made up more than 40 percent of the adult population were more than twice as likely to suffer civil conflict. That's according to a study by Population Action International, a research and advocacy organization concerned with family planning and reproductive health issues.

The Muslim world has been getting younger in recent years. The share of young males grew by more than 25 percent since the mid-1990s in countries including Pakistan, Iran and Saudi Arabia, according to Fred Pearce's recent book The Coming Population Crash.

That's helped create the conditions that led to rebellion in Egypt, Tunisia and other countries in recent weeks.

"The problems certainly transcend the youth bulge, but in all these places it starts out with youth discontent," says Ray Takeyh, senior fellow for Middle Eastern studies at the Council on Foreign Relations. "The original spark is usually the youth. Unless they're suppressed quickly, then it gathers other constituencies."

Less Cost, More Complaints

Young people are more prone to engage in civil disobedience for a couple of reasons.

For one thing, the risks for them are often smaller. Many do not have families that they have to worry about supporting from within a jail cell, for instance.

And their complaints are sometimes greater than their elders'. One effect of the recent downturn has been a spike in youth unemployment that is much greater than for the workforce as a whole. In Spain, the unemployment rate for people 25 and under peaked above 40 percent.

And this problem is particularly acute in Arab countries, where unemployment rates remain among the world's highest - and there are lots of young people.

"If you're a young person coming of age in a country with a large youthful population, your prospects often are not very good," says Elizabeth Leahy Madsen, a senior research associate with Population Action International.

Failing To Create Jobs

There are countries that have enjoyed a "youth advantage," Madsen says, by investing in education and putting their young people to work.

The most notable recent examples came in the 1980s and 1990s, when the East Asian "tiger" countries, such as Thailand, Indonesia and South Korea, were able to shift from agriculture to more knowledge-based economies by investing in their suddenly abundant human capital.

But most of the countries now experiencing a youth bulge - places like sub-Saharan Africa, parts of Latin America and Pakistan and Afghanistan - are not creating enough jobs to keep up with population growth.

In Arab countries, this has led to mass frustration. Many of the societies now under siege have invested heavily in the education of their young people, but have not provided them with enough to do after graduation.

That's particularly difficult for today's Arab youth, who are able to gain glimpses of how much their countries' economies are faltering compared with the rest of the world through social media, the Internet and satellite television.

"The youth component's crucial," says Shadi Hamid, director of research at the Brookings Doha Center. "They're the ones most affected by structural underemployment."

Hamid says underemployment can lead more readily to discontent than unemployment, because rising expectations are not being met.

"We're talking about people who are college-educated and ambitious and want to accomplish something with their lives," he says. "But the jobs aren't out there, so they have to be taxi drivers."

Take that individual frustration, multiply it millions of times, and conditions may be ripe for a country-wide rebellion.

"The youth here are like the wedge in a football formation," says Jack A. Goldstone, director of the Center for Global Policy at George Mason University and an expert on revolutions and population. "They are taking the lead, doing the most dangerous work. Behind them are the waves of shopkeepers, doctors, lawyers, mothers."

Not every Arab country has the same youthful mix. In Yemen, the average woman is still bearing more than six children. In Tunisia, by contrast, the fertility rate has plunged from more than five children per woman in the 1980s to less than two, which is a lower rate than in the United States.

"A country like Tunisia has a better chance, a demographic security analyst would say, than either Egypt or Yemen," where the rates remain high, Madsen says.

For now, the Arab youth bulge is very much a part of the mix of factors fueling protest. The fact that young people are not, by and large, being put to good use, is jarring traditional hierarchies and the cultural willingness to accept one's place.

"It's almost become a cliche, that there's a youth bulge in the Arab world," says Geneive Abdo, an analyst with the National Security Network and the Century Foundation. "We never realized what the effect of that would be, until now."