Imagine an alternative America for a moment, in which the black minority had ruled for hundreds of years. Whites were excluded from public office, rarely allowed in the police or Army and largely disenfranchised. Jails filled to bursting with whites suspected of plotting against the black regime. Hispanics were discriminated against as well, targeted for massacre by poison gas, until a successful rebellion in the Southwest led to a self-governing Latino enclave around New Mexico, Arizona and southern California. A black dictator ran the rest of the country with such savagery that a foreign power toppled him, on the second try.

It's easy to see where this rough analogy is going. It works well enough to help understand the depth of the enmities and passions underlying the crisis of an Iraqi transition from Sunni to Shia rule, with Kurds as the wild-card minority, and the difficulties of imposing a peaceful solution whatever the outcome of elections planned for Jan. 31, 2005. Many if not most Sunnis are likely to boycott, and extremists will do all they can to sabotage the vote. Sunni Arabs in Iraq are only some 20 percent of the population, but they're its traditional rulers; the Shiites, with 60 percent of the population, have been downtrodden for centuries, not just during Saddam Hussein's regime.

Analogies go only so far, of course, and there are many fundamental differences in the culture and history of the two societies. In some ways, the divisions in Iraq are even worse than racial tensions in America, because religion is involved. It's as if, in the scenario above, all the ruling blacks were Protestants and all the whites Roman Catholics, subject to imprisonment for crossing themselves in public. And now the occupying foreign power has ordered the Protestants, who are taught from childhood that Catholics are blasphemers (as Sunnis have long viewed Shiites), to join a government dominated by those Catholics.

The marvel is that civil war has not already started. But the hiatus is temporary and artificial. As long as American troops are present in strength, they give Sunnis and Shiites another focus for their anger. But particularly in the Sunni radicals' view, there is little appeal in a democracy likely to be dominated by Shia religious figures.

Unlike the Sunni, the Shia have a strict religious hierarchy. Leaders like Ayatollah Ali Sistani and the other clerics of the Howza, the council of the leading ayatollahs in Iraq, have immense influence. Fortunately, Sistani is a moderate, and moderates dominate the Howza as well; they've made it clear that they have no interest in creating an Islamic republic, as the Shia in Iran have done. Sistani rules out a political role for clerics, including himself, but his concept of politics is a narrow one. Clerics should, he has written, provide spiritual guidance, and that extends to fatwas ordering people to vote, to participate in government or not, even to resist publicly some decision of the government. What they eschew is holding political or administrative office.

But this nuance doesn't comfort Sunnis, who are well aware of the Shia tradition of Taqiya, a religious doctrine that grew up from centuries of harsh discrimination by the Sunnis who hold sway in most Muslim lands. It means "dissimulation," and allows the Shia to hide their true intentions, even to follow alien religious practices, if that's what it takes to survive.

Increasingly, terrorists like Abu Mussab al Zarqawi and others have been hijacking the Sunni resistance. Partly that's because, lacking the religious hierarchy of the Shia, the Sunnis have no natural moderate leaders, except those tainted by their cooperation with the occupation authorities. But it's also because the terrorists are the only ones who dare to articulate the deep Sunni fear of the majority Shia, and the only ones to act against them.

And while they lack moderate leaders, the Sunnis have plenty of foreign friends. Jordan, Syria and Saudi Arabia are all Sunni countries with long and difficult-to-defend borders with Iraq. They're a source for volunteer fighters and money. "Zarqawi and his followers have no shortage of funds," says a senior Western official in Baghdad. Powerful hard-liners in those countries sympathize with the Sunni resistance and are deeply concerned about the possibility of a Shia-ruled Iraq, and the axis that would create with the Arabs' traditional enemy of Iran.

Saudi Arabia has a large and long-downtrodden Shia minority of its own, predominantly in the oil-rich Eastern province. Jordanians have strong tribal links with the Sunnis, especially in the rebellious western Anbar province, and in Mosul in the north. The Syrians share the ideology of the Baathists who ruled Iraq until Saddam's overthrow. Syria and Iraq were once enemies, but their differences were less over ideology than over personality, particularly Saddam, and that problem is gone.

The Kurds, meanwhile, sit quietly on the sidelines--for now. They've never been victims of the Shiite majority. Since 1991, they've lived in relative safety and prosperity in their northern enclave. Relative autonomy has been the source of their safety, and they're not going to give that up easily, even to a Shia government. The Kurdish issue may well be the first spark that ignites a true civil war in Iraq. The match may be the struggle to control the city of Kirkuk, now in the Kurdish zone. No central government, Shia or Sunni, is going to want an autonomous Kurdistan if it includes the oil wealth of Kirkuk.

One solution that has been floated in Baghdad is the dismemberment of Iraq into a Shiite south, a Sunni center and west and a Kurdish north. One high-ranking interim-government official and former proponent of a united Iraq was, by the end of 2003, saying he saw partition as the only hope. That's a solution none of Iraq's neighbors can accept, and most of its natives would not, either. The traditional Sunni areas are bereft of natural resources. The Shia are present in largenumbers in Baghdad (where they may be more than half the population, and there is some intermarriage) and in many of the cities of the Sunni Triangle. And the Shia haven't suffered all these years to come into political majority and lose two thirds of their country. Only the Kurds would opt for independence--if they could manage not to engage in their own civil war (as they did most recently in 1994).

The new government in Iraq, however legitimate this January's elections, will have its hands full slowing the slide toward civil war. It will convene a constitutional convention to define the rights of each faction, while fighting a Sunni rebellion that will likely continue to grow. To gain legitimacy, it will have to divorce itself somehow from the American military, on which it will depend for its continued existence. Other options, like bringing in the Europeans or the United Nations, are highly unlikely to happen under a Bush administration. Another possibility is that the Americans leave prematurely, before another set of elections scheduled for the end of 2005. Either way, it means the very great likelihood of civil war in Iraq--either the sort of low-level civil war of insurgents and terrorists against an American-supported government, or else the bloody free-for-all that would ensue if Iraqis don't agree on a political framework acceptable to all major factions. The United States went to war with itself in 1861 as the outcome of far less provocation. Why should we expect any better of the Iraqis?