To the outsider, the differences between the Sunni and Shiite Islamic sects are hard to recognize.
The five pillars of Islam – daily prayer; fasting during Ramadan; alms giving; the pilgrimage to Mecca; and belief in one, unitary god – are at the core of both faiths, and most mainstream clerics in each denomination recognize adherents of the other side as "legitimate" Muslims.
The Koran is the sacred text for both. They believe Muhammad was the prophet and that there will be a resurrection followed by a final judgment when the world ends.
Adding to the potential confusion is the insistence of many Muslims not to be identified as Shiite or Sunni, saying they are Muslims and Muslims only.
But, as recent events in Iraq and Lebanon have shown, the differences between the believers are not only seen as important by the communities but now, as they have for centuries, rest at the core of bloody political struggles.
While there are superficial differences between the sects – differences in prayer and carrying out ritual ablutions, for instance – the arena of conflict between the two has long been political.
The split between the two main branches of Islam is nearly 1,400 years old, and started with a fight over who should lead the faithful after the prophet Muhammad's death in 632. One side believed that direct descendants of the prophet should take up the mantle of the caliph – the leader of the world's faithful. They were known as the Shiat-Ali, or "partisans of Ali," after the prophet's cousin and son-in-law Ali, whom they favored to become caliph. In time, they came simply to be known as Shiites.
The other side, the Sunnis, thought that any worthy man could lead the faithful, regardless of lineage, and favored Abu Bakr, an early convert to Islam who had married into Muhammad's family. "Sunni" is derived from the Arab word for "followers" and is shorthand for "followers of the prophet."