The new assertiveness of Iraq's Shiite Muslim majority has raised worries elsewhere in the mostly Sunni Muslim Middle East, where governments fear the rise of an Iranian-style theocracy, unrest at home and revived tensions within the family of Islam.
Saudi Arabia, with its own significant Shiite population, may feel among the most threatened by events in Iraq, its neighbor to the north. But even farther afield in places like Egypt, there is concern about what is seen as Shiite restiveness.
"Now the game is how to contain it," Egyptian political scientist Gehad Auda said.
Sunnis are by far the majority of the world's more than 1 billion Muslims, but in Iraq they make up only about a third of the 24 million people. Most of the rest are Shiite.
Saddam Hussein's regime was dominated by Sunnis. Now that his regime has been toppled by U.S. and British forces, Shiites are bursting forth to make clear they expect more say in Iraq's political future.
This week, an annual ritual that was repressed by Saddam's regime became a display of Shiite power as hundreds of thousands made a pilgrimage to the central Iraqi city of Karbala to commemorate the 7th century martyrdom of the Prophet Muhammad's grandson Hussein. While performing the ritual, many pilgrims shouted anti-U.S. as well as anti-Saddam slogans.
"The end of Saddam the tyrant has awakened the Shiite giant in Iraq," Saudi political analyst Khaled bin Sulaiman al-Sulaiman said Wednesday.
Auda predicted that nations in Iraq's neighborhood would try to slow political reforms the United States envisions that could result in Iraqi Shiites voting themselves into power.
"Democracy wouldn't serve the purpose of containment," Auda said.
He expects Saudi Arabia to work with countries like Egypt, whose status as the largest Arab country and a key U.S. ally gives it political muscle in the region, to try put its own stamp on Iraq's future.
Egypt's government may feel it has to act to calm Sunni fundamentalists, a growing political force in Egypt, Auda said. Sunni fundamentalists are deeply suspicious of Shiites.
In Egypt, where Shiite traditions are largely unknown, bloody television and newspaper images this week of Iraqi Shiites slashing their bodies and crying out in a stylized display of mourning for Hussein were viewed by many with baffled distaste.
Shiites are more visible in Saudi Arabia, making up 10 to 15 percent of the kingdom's roughly 19 million people, but they complain of restrictions on their freedom of expression, inability to advance in government jobs and other discrimination. The divide is deepened by a puritanical Sunni code in Saudi Arabia that shuns not only other religions but also other Muslim sects.
In the 1980s, Saudi Arabia was convinced that mostly Shiite Iran planned to spread its 1979 Islamic revolution and exploit the complaints of Saudi Shiites. The kingdom and other Arab states supported Saddam in his 1980-88 war with Iran.
In 1988, Saudi Arabia broke relations with Iran, accusing it of supporting terrorism and subversion. Relations were restored shortly after the 1991 Gulf War, but suspicions are being revived now that Iran is seen as meddling in Iraq, its neighbor to the west.
Islam has been divided into the orthodox Sunni and minority Shiite sects since soon after the death of the Prophet Muhammad in 632. Sunnis accepted Abu Bakr, a respected contemporary of the prophet, to lead what was then an international political as well as spiritual empire.
A small group, the "shi'at Ali," or party of Ali, followed the much younger Ali, Muhammad's cousin and son-and-law.
In one 7th century battle rooted in the dispute, Hussein, Ali's son, was killed by Sunni rivals on the plains of Karbala in what is now Iraq.
The bloodshed has continued even in modern times.
Sunni, Shiite and Christian militias all fought each other during Lebanon's 1975-90 civil war. In the Gulf state of Bahrain, where Shiites are a slight majority but the ruling family is Sunni, Shiites staged a violent campaign for political reform in the 1990s, triggering a government crackdown.
Lebanon's war ended when a power-sharing deal was struck under which the president is always Maronite Catholic, the prime minister Sunni Muslim, and the speaker of parliament Shiite Muslim. Calm came to Bahrain when the emir bowed to demands for more democracy that gave Shiites a say in politics.
The Bahraini and Lebanese examples showed that the Sunni-Shiite rivalry can be peacefully resolved. Ali Fakhro, a former Bahraini minister of education and a Sunni, said he believed all Iraqis understand that if they fought each other, the U.S. and British troops that ousted Saddam would linger, denying Iraq its independence.
"I think both Sunnis and Shiites realize these cards should not be given to the American occupiers for the exploitation of Iraq," he said. "I have great faith in the Iraqi people and I think its time they are allowed to decide their own fate and live united."