Pakistani Muslims buy balloons for their children after prayers in Karachi, Pakistan, in July. (Fareed Khan/AP)

This week, I reported a story for The Post from Jakarta on the “Muslim youth bulge” — the surge in youth in the Muslim world — and explored why this could be a recipe for instability. As a journalist and a young person (I’m 26), I’m fascinated by how young people shape society — sometimes for better, sometimes for worse.

One thing that’s very clear from academic literature on demography and social change is that young people matter. When they feel that the system is stacked against them, they tend to demonstrate — think of Occupy Wall Street, and of how “We-need-a-political-revolution” Bernie Sanders won 70 percent of the youth vote in the Democratic primaries.

What’s clear, though, is that in societies that aren’t democracies, young people who are disappointed by their lack of opportunity have fewer outlets by which to peacefully effect political change. One reason, then, for apprehension about the huge size of the Muslim world’s youth population is that much of this growth is happening in its least developed parts, where there are the fewest opportunities for peaceful political expression.

In the Sahel — the band of countries from Mali to Sudan that borders the Sahara — governments are repressive and birth rates are extremely high.

Bad government institutions combined with growing desertification due to global warming mean youth here will grow up with few opportunities. They’ll likely respond to this in myriad ways. Some might try to immigrate to wealthier countries; others may lower their expectations for life and try to make what they can of it, others will join up with the army or terrorist or guerrilla groups. But these countries' young people will — by and large — have pretty bad options, and many won’t accept them sitting down.

So, at a time when headlines are filled with stories of young Muslim men fighting each other, one reason why it’s helpful to consider the population structure of the Muslim world is that doing so helps to emphasize the “young man” aspect of the instability rather than the “Muslim” aspect.  After all, just because Islam is the primary form of political expression for youth frustration in the Middle East and North Africa doesn’t make it the primary cause of the violence. Young people with few opportunities explains a lot of it.

Here we can see how much younger the world’s Muslim population is compared with its Christian population.

Another interesting phenomenon revealed by the data in a 2015 Pew study is that in virtually every case where Muslims and non-Muslims live side by side, Muslim populations skew younger, owing to a higher birthrate.

This suggests that there are factors related to how Islam is being interpreted that contribute to large family size. One exception is Indonesia, where the Eastern, mainly Christian part of the country is less developed than the rest of the mostly Muslim archipelago and has a slightly higher birthrate.

In this chart, which compares the average age of Iran and Afghanistan, we can see the age difference between Iran, which embraced birth-control policies decades ago and has one of the highest average ages of a Muslim-majority country, and Afghanistan, which has one of the lowest.

This disjuncture in Iranian and Afghani average age helps explain why Iran has been hiring thousands of Afghan young men from the Shiite Hazara minority to fight for the Iranian-supported Assad regime in Syria. The costs of recruiting an Afghan man to fight are much lower than the cost of recruiting an Iranian man, who is more likely to be educated and have better opportunities than fighting for $500 a month in a conflict far, far away.

“Most go for the money,” an Iranian recruiter of Afghan men told the Guardian. The moral of the story is that it’s easy to lure young men with few opportunities to fight, and harder to persuade young men with more opportunities to fight. This is one reason why countries with youth bulges can be more violent; the opportunity costs for a young man to pick up an AK-47 are often lower.

What all this suggests is that instability gripping parts of the Muslim world may have less to do with ideologies that promote violence, and more to do with the high proportion of youth. Of course, one reason why Muslim societies have stubbornly high birthrates could be owing to ideology.