The battles that erupted last week at Islam's holiest shrine during the most sacred occasion of the year, culminating in 402 deaths, have roots as much in the past as in the present. The different historic legacies and religious interpretations of Islam's two main sects - Sunni and Shia - explain why the tension is likely to persist.
The schism began 13 centuries ago as a political dispute over who should lead the Islamic empire - a dispute played out again last week between Iran's Shiite pilgrims and Saudi Arabia's Sunni security forces. Both sects claim authority over the Islamic world, or one-fifth of mankind.
The 7th century schism and its immediate aftermath established the mindset of martyrdom, the sense of persecution, and the zealotry among Shiites that have played a role in contemporary Mideast politics. Those ancient attributes combined with recent political developments to become explosive in Mecca.
Religion has always had a larger role in the life of Muslims than in any other major world faith. Islam provides a political system, complete with rules of law, as well as a religion. And politicization is strongest among the Shiites.
Briefly, the Shia, now roughly 10 percent of the world's 850 million Muslims, wanted leadership to descend through the family of Islam's founder, the prophet Muhammad. Their candidate was Ali, the son-in-law and cousin of the prophet, who eventually became the fourth caliph, or God's representative on earth. The name Shia comes from Shiat Ali, or followers of Ali.
But after Ali was murdered, the caliphate passed to the ancestors of today's Sunnis, now almost 90 percent of the Muslim world.
Most important to Shiite tradition was the attempt in AD 680 by Hussein, Ali's son and Muhammad's grandson, to defend his line's right to the mantle of the prophet. He had a small band of under 100. The caliphate, based in today's Iraq, had thousands of troops.
Hussein's group was massacred, but for them it was more honorable to die for belief than to live with injustice. Hussein became the supreme martyr, the symbol of man's struggle against tyranny - a precedent that not only survived, but grew in importance over time.
His symbolic act is at the root of Shiite beliefs that they are victims of authority and persecution, and that they have a duty to God to revolt against temporal authority. Martyrdom is the most honorable defense of their faith. And the Shiites genuinely believe their acts, viewed as terrorism by Sunnis and by Western nations, are a defense - are in response to others' aggression.
Events in Mecca coincided with several factors accentuating the Shia feeling of being on the defensive again.
First, US warships had just been deployed in the Gulf. Iran felt it was being unjustly blamed for disruptions in shipping and unfairly threatened by the US fleet, particularly since both nations share an interest in freedom of navigation. Unlike Iraq, which can export its oil via pipelines through Turkey and Saudi Arabia, Iran has only the Gulf for exports and for imports. Cutting off Gulf traffic would have a far more devastating impact on Iran than Iraq.
Also, the ``tanker war,'' which erupted in 1984, was begun by Iraq. Even the US State Department has acknowledged that Iran has shown comparative restraint in retaliatory strikes. Each escalation in the past three years has been by Iraq; whenever Iraq stopped its attacks, so did Iran. That is not the kind of behavior, Tehran feels, which warrants deployment of US warships.
Second, tension in the Gulf coincided with two domestic crises: an increasingly bitter internal power struggle and the deep embarrassment of leading members of Iran's theocracy by revelations from the US's Iran-contra hearings.
Iranians involved in the affair were repeatedly humiliated during the hearings. Lt. Col. Oliver North's statement, for example, that he repeatedly lied to his Iranian counterparts seemed to prove that the US was duplicitous - as militant Iranian factions had always claimed. The timing, which coincided with escalating internal squabbling, forced those who favored normalizing Iran's status in the international arena into a corner. As is the Shiite way, they came out fighting. Parliament Speaker Hashemi Rafsanjani, whose supporters were deeply implicated in talks with the US, has recently been among the most outspoken critics of the US. A key member of his faction played a major role in organizing the anti-US demonstrations that led to the clashes in Mecca.
Another key difference between the Shia and Sunni - the role of leadership - was evident during the Mecca confrontation. Shiite clerics have far more power in mobilizing their followers than do Sunnis, since the Shia believe the clergy interprets God's laws and wishes for man. For Sunnis, man's relationship with God is direct; clerics serve mainly as advisers.
Thus when Ayatollah Khomeini urged Iranians to challenge Saudi authority over Islam's holy places as well as the legitimacy of the pro-US Saudi monarchy - as he did in a series of speeches before the annual hajj pilgrimage - his followers took heed.
Monarchy as a system of government is anathema to Ayatollah Khomeini's brand of Shiism. Iran, the only nation with a Shiite government, also feels it has a symbolic obligation to challenge the Sunni guardians of Islam's holiest sites.
Thus the Mecca tragedy has long been coming. It was not the first clash involving Shia and Sunni rivals nor, in light of the growing number of potential flashpoints in the Middle East, is it likely to be the last.
Ms. Wright, a former Monitor correspondent, is a senior associate at the Carnegie Endowment for International Peace. She is author of a book on militant Islam.