Many believe that an ancient religious divide is helping to fuel the conflict in the Middle East and Muslim countries.
So how can one religion be so divided along ideological lines?
This article by the Council on Foreign Relations provides a simple yet comprehensive explanation of the Sunni-Shia divide which seems to be having such a profound impact on the world today.
The Council on Foreign Relations is a leading, nonprofit US think tank that specialises in foreign policy and international affairs. You can read more about them at their website.