As Geography@About.com pointed out China will have 30,000,000 more young men then women by 2020. The reason for such a gap is Chinese have been having more abortions on baby girls then boys due to old cultural bias against girls. So where will these 30 million men place their angry sex-deprived lives? Most likely the military. And with Chinese military having the reputation that it does, many observers are worried.
India has a similar trend of aborting more girls than boys and this is placing strains on the culture.
Finally in the Muslim world there is a large increase in the youth population. About third of Jordan and Egypt and nearly half of Somalia and Afghanistan are under 15 (compared to 20% in the United States). This has social scientists like Gunnar Heinsohn worried. Heinsohn's "Youth Bulge" theory, too many young people leads to an increase of crime, war, terrorism, etc, is being applied to the state of the world today.