When hundreds of thousands of black-clad Shiite pilgrims set out on foot early this year, they risked their lives on bomb-rife roads as they walked hundreds of miles to the holy destination of Karbala. To outsiders, these Iraqis may have seemed to harbor a death wish. To them, of course, they were fulfilling a religious duty. They were off to commemorate Ashura, the 10-day mourning period honoring the martyrdom of Imam Hussein.

Scores of Shiite pilgrims died in Ashura blasts this year alone — blasts believed to be engineered by Sunni insurgents — and it's this centuries-old internecine conflict that Lesley Hazleton brings to light in her new book. Written in an easy and accessible narrative, the Middle East journalist tidily reconstructs a chapter in the long and battle-weary history of Islam, from Muhammad's death in 632 to the clashes over naming his successor to the brutal slaying of Imam Hussein in Karbala. The Shiite-Sunni story fights conclusion.

"The Karbala story is indeed one without end, still unfolding throughout the Muslim world, and most bloodily of all in Iraq, the cradle of Shia Islam," Hazleton writes.

ILLUMINATING DETAILS

After a prologue that briefly retells what came to be known as the Ashura Massacre in Karbala in 2004, Hazleton takes her reader back to the origin of the wide-scale bombing: Muhammad's death, of natural causes at 63, and the absence of a successor. Though the prophet had multiple wives, he had no sons to whom he could pass his legacy.

And so sharp divisions between Shiites and Sunnis emerged, the former believing cousin Ali had been chosen to lead, the latter holding that the community picked the Muhammad confidant and caliph Abu Bakr. This book is about the dangers of interpretation and the power of symbols.

The Shiite-Sunni split in seventh-century Arabia may seem readily familiar to Islam and Middle East scholars, but the book is almost certain to educate lay Western readers about the history of the world's fastest-growing religion (and, let's hope, policy makers). After all, Islam didn't occupy the same place in the Western imagination as it does in these post-9/11, post-2003 Iraq invasion times.

Illuminating details abound. Hazleton notes that four out of five Muslims are not Arab. Shiite Muslims, while now at the helm in Iraq, make up 15 percent of Islam's worldwide population but close to half in the Middle East. Before appointing himself supreme leader, Khomeini invoked the Karbala story in the Iranian Revolution in 1979. And the region's oil on which the West depends so much fuels the same Sunni insurgency that attacks Western armies.

MIDDLE EAST PRIMER

Indeed, "After the Prophet" will be held up as a primer for grasping the modern-day Middle East — mainly in Iraq but Iran, too. Understand the history, Hazleton's book suggests, and you understand why somebody would pack a truck with explosives and ram it into a shrine. It's a well-known premise, but reminders are useful.

A 2006 attack on the Askariya Mosque in Samarra — Sunni extremists al-Qaida in Iraq, the suspected culprits — resonates with meaning in the aftermath of similar attacks on Shiite shrines. "Attack the Askariya shrine in Samarra, and you commit something even worse: you attack the Mahdi ("one who guides divinely") and thus the core of Shia hope and identity," Hazleton notes. "The destruction of the Askariya shrine was an attack not just on the past, or even the president, but on the future."