The sheer number of inhabitants doesn't tell the whole story yet. The demographic structure is very important. Youthful societies tend to be more aggressive, especially the poor ones.
"Recent studies suggest that a large 'youth bulge'—a youthful population age structure—can increase the risk of the onset of civil conflict and political violence (Urdal, 2006, Cincotta et al., 2003). These studies exclude states with a recent history of civil conflict, reasoning that they are already highly vulnerable to persistent and re-emerging violence (Collier et al., 2002). Can these two quantifiable variables—population age structure and recent history of civil unrest—be used to project risks of civil conflict a decade into the future?"
The answer is 'yes'. All the recent hotbeds of terrorism are youthful societies where an aggressive ideology has worked as a fuse. Take Gaza, Syria and Iraq as the most salient examples.
According to the same source (emphasis mine):
This population phenomenon, called 'youth bulge,' is especially prevalent in fragile states and Africa. (...)
A young population can drive national growth, if the government and economy are strong enough to provide opportunities for upward mobility and financial independence. The problems begin when a young labor force finds itself unemployed, restless, poverty stricken, and uneducated. In recent years, countries with young populations have proven especially vulnerable to conflict, extremism, and civil strife. Of the 67 nations currently experiencing youth bulges, 60 are also experiencing civil unrest and conflict."
Source: The Wilson Center
I would love to know the answer to the problem, but I don't.