The show continues their series, “TODAY's 101,” with help from Vali Nasr, author of “The Shia Revival: How Conflicts Within Islam Will Shape the Future.” In his book, he provides an understanding of the 1,400-year struggle between Shias and Sunnis, and sheds light on its modern day consequences. Read an excerpt:

Chapter 1
The Other Islam
Who Are the Shia?
Every year on the tenth day of the holy month of Muharram, the first on the Islamic lunar calendar, Shia Muslims show a distinctive face of Islam, one that sees spirituality in passion and rituals rather than in law and the familiar practices that punctuate Muslim lives. Open spaces and narrow alleys in cities, towns, and villages take over from mosques and seminaries as Shias individually and collectively make a show of their piety and their identity. No observer of this day, the festival of Ashoura, will remain unaffected by the Shias’ display of fealty to their faith. None will fail to see the uniqueness of Shia Islam or the values and spirituality that define it.

Every year on this day — whose date on the Western calendar changes from year to year because of differences between the Gregorian solar reckoning and the lunar months of the traditional Muslim calendar — the Shia mark the anniversary of the death of their most vividly recalled saint, the grandson of Prophet Muhammad known among the Shia as the Imam Husayn. The day is called Ashoura, from the Arabic word for “tenth.” It is an occasion for collective atonement through lamentation and self-flagellation. It is a distinctly Shia practice and has no parallel in Sunnism. In those areas of the Muslim world where Shias and Sunnis live side by side, Ashoura underscores Shia distinctiveness and often draws Sunni opprobrium. Ashoura is a day when the Shias announce who they are — often going to great extremes to do so—and when the Sunnis, by condemning and protesting, in equal measure may announce their objection to Shia practices.

When Ashoura falls on a warm day late in the spring, throngs of Shia women and children line the narrow byways of the old city of Lahore, a medieval village now surrounded by the sprawling bustle of modern urban Pakistan. Old Lahore’s meandering streets (too small for cars), its antique villas with their high ceilings, graceful courtyards, and jutting verandas, and its ornate mosques and towering gates take a visitor back centuries, to the days when the Mughal emperors ruled these lands. On one side of the old city sits the grand Badshahi (Royal) Mosque. Arching gates mark each of the four main passages into the old city’s humming bazaars. To the discerning eye of the knowing pedestrian, the old city reveals itself to be a Shia settlement, dotted with small shrines and places of worship dedicated to Imam Husayn.

NBC VIDEO Author discusses conflicts within Islam Feb. 23: TODAY host Meredith Vieira talks with Vali Nasr, author of "The Shia Revival: How Conflicts Within Islam Will Shape the Future," as part of the show's series on understanding the Middle East. Today show

Each quarter of the old city has its own Ashoura procession. They compete and converge as they wend their way through the streets, visiting every one of those mosques and places of worship. At the head of each procession marches a group of young men carrying a tall metal staff ornately decked with thin strips of red, green, and white cloth that flutter and snap in the breeze. High on the staff sits a triangular black pennant. Above it, at the very top, is the elaborately carved shape of a human hand. The hand represents the five holy people whom the Shia hold in highest regard: the Prophet Muhammad, his daughter Fatima al-Zahra, his son-in-law and cousin Ali, and his grandsons Hasan and Husayn. The hand and the black flag mark Shia houses, mosques, and processions from India to the Middle East.

Young boys offer water to the watching crowd. Everyone drinks and says a prayer for the martyred Husayn. Behind the men carrying the staff comes a riderless white horse with a beautiful saddle on its back and white feathers on its drooping head. The horse is the center of attention. Its empty saddle reminds watchers of its fallen master, the object of the crowd’s adulation. Several women, their heads covered with scarves, trail the horse, gently beating their chests and chanting “O Husayn!” They are praying for forgiveness, for on this day, the Shia believe, God answers prayers and forgives the repentant more readily than on any other day—regardless of either the nature and number of the sins committed or the penitent’s degree of adherence to the daily practices that characterize Muslim piety.

Some of the women are weeping. The atmosphere is charged with anticipation. From around a bend in the street comes a rhythmic thudding interspersed with chanting. Then the bulk of the procession, a long line of men, heaves into view. Dressed in black, they walk four abreast and fill the narrow alleyway. Following the lead of an older, white-bearded man up front, they beat their chests with both hands as they chant and call in unison, “Ya Husayn!” As the procession passes, the sounds of the voices and the thumping echo from the old city’s ancient walls.

The sights and sounds of Ashoura are gripping. This is a ritual filled with symbolism and passion. It is deeply spiritual and communal. It defines Shias and renews their bond to their faith and community. It reminds believers that the essence of their religion is not works but faith. With some local variations, the same ritual will be taking place on this day in the Indian city of Lucknow, the Iranian capital of Tehran, Karbala in southern Iraq, the island country of Bahrain in the Persian Gulf, and the town of Nabatiye in southern Lebanon. Ashoura is an act of piety, but not one that is recognized as an obligatory practice of the faith. It has no foundation in the Quran and was not practiced at the time of the Prophet. Yet this is also Islam, even if not in a guise that most Westerners readily associate with the religion.¹

So what is Shiism? And what separates the Shia from the Sunni? Most Western discussions of Islamic matters or the Arab world tend to focus, often implicitly, on Sunnism. This is perhaps to be expected, since the overwhelming majority of the world’s 1.3 billion Muslims are Sunnis. Shias number from 130 million to 195 million people, or 10 to 15 percent of the total.² In the Islamic heartland, from Lebanon to Pakistan, however, there are roughly as many Shias as there are Sunnis, and around the economically and geostrategically sensitive rim of the Persian Gulf, Shias constitute 80 percent of the population.

MORE FROM TODAY BOOKS: HISTORY POLITICS

Whatever happened to ‘Patriotic Grace’?

Whatever happened to ‘Patriotic Grace’? Bush, McCain and an infamous hug Excerpt: Roald Dahl’s secret mission Book reveals secret Iraq mission, more Excerpt: Why we drive the way we do Capturing the essence of ‘Mandela’ ‘Rome 1960': Politics at play in Olympic Games In ‘Your America’ average citizens take action ‘Fleeced’ vows to pull the wool off taxpayers’ eyes Journalist captures ‘Bobby Kennedy in the Sixties’   Add Today Books: History Politics headlines to your news reader: