While the US and Europe have remained fixated on the simmering sovereign debt crisis in Euroland, the Arab world has been experiencing waves of demonstrations, protests and civil wars that have seen the fall of three major regimes thus far in 2011, with several others struggling to find equilibrium.

The underlying forces behind the Arab Spring are complex and vary from country to country. But a key factor is demographics, as a glance at the population pyramids below suggests.

A common denominator of the three is an aging ruling party unable to control a population bulge of young adults afflicted by high unemployment, food inflation, corruption, an absence of political freedoms and generally poor living conditions.

The three pyramids above differ somewhat from one another, especially the pattern of contracting growth in Tunisia. But the three exhibit the common demographic of young adult males in the numbers necessary to mount a successful overthrow of the government.

Earlier this month I posted a commentary on Boomer Demographics: The Shift Ahead, which was an outgrowth of my presentation at the Retirement Industry Income Association (RIIA) 2011 Fall Conference.

My focus on demographics, as in the Boomer piece, has generally explored the financial implications of an aging population on government debt and the slow-motion ripple effect on markets and the economy. I'll have more on this topic next week in some commentaries on world demographics, especially Europe. But sometimes the impact of demographics can be sudden and explosive, as we've seen in the Arab Spring.