Shia

Do you have this problem related by the Onion? If so, the Shia Revival is probably a good choice for you. The Shia-Sunni split is often compared to the Catholic-Protestant split in Western Europe. As the book shows, the analogy only goes so far. For one, the split took place twice as long ago and it is bound up not only in theological terms, but in socio-political terms such as how can be said to rule on Earth. The author, Vali Nasr, details the centuries long dispute and the frequent atrocities both sides committed against each other.

From a current policy perspective, understanding how the Sunni and Shia differ and how they interact is critical to understanding the state of Iraq and the great risks of conflict with Iran. The book is biased towards the Shia point of view, which you have to take in mind, but it is helpful to the Western reader as this sect is often demonized in the Western press. The book also helps explain the role of religous leaders in places like Iran and how politics differ in that country.

And if you really want some indepth info, check out this Brookings report on containing the Iraqi Civil War. It's sobering reading.