Syria has arrived at a tipping point. After months in which the regime of President Bashar al-Assad clearly held the dominant hand, the forces arrayed against him have now multiplied to the point where a serious battle is possible.

The resistance increasingly is armed and taking on the regime, even controlling towns and villages. The Arab League has abandoned tradition to fully support the opposition. And at the United Nations, only Russia and China stand in the way of a resolution calling for Assad to go.

The stakes for Syrians and the Mideast in general go well beyond how democratic Syria may become after the fighting ceases. According to the prevailing narrative, the recent revolutions in the Arab world are battles between the forces of authoritarianism and freedom. But it is the long-running rivalry between the Shiite and Sunni factions of Islam that is the dominant dynamic in the region today. Syria is ground zero in the sectarian great game consuming the Middle East.

Among the manifestations of this phenomenon are the pro-democracy protests in Bahrain last spring that quickly turned into a sectarian clash between the Sunni monarchy and the majority Shiite population. The prospect of a neighboring kingdom falling under Shiite rule so alarmed the Sunni rulers of Saudi Arabia, they sent troops to Bahrain in an effort -- not entirely successful -- to end the unrest. That move aggravated tensions between the Saudi government and that of Shiite-majority Iran.

Brutal Bombing Campaign

In Iraq, sectarian posturing trumped talk of national unity the moment the last U.S. troops exited the country in December. Sunni parties broke with the Shiite-dominated government, and Sunni extremists resumed their brutal bombing campaign against Shiite targets.

Lebanon, once the archetype for sectarian mayhem, is again simmering with Sunni-Shiite tensions. Sunni political parties have been in a constant state of conflict with the Shiite party Hezbollah after it strong-armed the Sunni government of Prime Minister Saad Hariri out of office last year, replacing it with its own choice of Sunni leader. That resulted in a lack of justice for the 2005 murder of popular Sunni Prime Minister Rafiq Hariri, for which a UN-backed tribunal blamed four Hezbollah members.

Among other factors deepening the region’s sectarian divide are the rise in Egypt, Jordan and Syria of Salafi forces, who espouse a very narrow definition of who is a Muslim and are deeply anti-Shiite; Iran’s resentment that some Sunni-led Arab governments support U.S. pressure on Iran; and Turkey’s newfound interest in speaking for the region’s Sunnis.

Yet nothing is as explosive as the situation in Syria. And what happens in Syria won’t stay in Syria, which is why so many other parties are trying to influence the outcome there. For the past four decades, Syria has been ruled by the country’s Alawite minority, adherents of a subset of Shiism, who have denied power to the majority Sunnis. In that sense, Syria today is a mirror image of Iraq before the U.S. invasion. Syria’s Sunnis, like Iraq’s Shiites in 2003, stand to gain from regime change, while Syria’s Alawites, like Iraq’s minority Sunnis at that time, are clinging desperately to power.

The predominantly Sunni opposition in Syria is backed by the region’s principal Sunni power brokers: Saudi Arabia, Turkey and Qatar. This, once again, has pitted Iran against Saudi Arabia. And it has clouded relations between Iran and Turkey.

Blow to Iran

The Sunni axis, backed by the U.S. and its European allies, wants to see Assad fall and a complete change of regime. This would be a strategic blow to Iran and Hezbollah and would strengthen the position of Turkey and Saudi Arabia in the region. A Sunni-dominated Syria would truncate the “Shiite crescent” that connects Iran, Iraq and Syria and extends into Lebanon via Hezbollah. Some Saudis go so far as to think that, combined with U.S. pressure on Iran, this would end the Shiite threat to regimes in the Persian Gulf.

The Shiite axis, meanwhile, hopes to keep Assad from falling. Iraq’s Shiite Prime Minister Nouri al-Maliki even pleaded his case to U.S. President Barack Obama during his recent White House visit.

It’s difficult to imagine the Syrian resistance giving up on its push to knock Assad off his pedestal. At the same time, a quick collapse of his regime seems unlikely. More probably, Syria will continue to slide gradually into civil war. Warring cantons backed by rival regional blocs may emerge. The resultant bloodshed, sectarian cleansing, refugee crises, assassinations and bombings could destabilize the whole region.

Iraq would be at particular risk. The country’s sectarian wounds remain open. Sunnis there are unhappy. Encouraged by events in neighboring Syria, they once again are turning to insurgency to secure their future. Iraq’s Sunni tribes already are major arms conduits for Syria’s rebels. The Sunni insurrections in Syria and Iraq could combine to create a dynamic infecting a zone from the Persian Gulf to the Mediterranean.

Given these terrible scenarios, the U.S. and its European allies must consider a way out that mitigates these risks. One option would be to have Assad go but “Assadism” remain. Yemen offers a precedent. Last year, amid unrest in Yemen, Saudi Arabia persuaded President Ali Abdullah Saleh to give up power in exchange for immunity from prosecution, while his clan remained firmly in control. The Arab League has hinted at such a resolution for Syria, though so far there is no international support for it.

Having Assad exit with his regime intact could stop the violence and give Syria an opportunity to reform. Achieving that would require the U.S. and its partners to work closely with Russia, which has a relationship of trust with Assad. The Russians would need reassurances that post-Assad they would be able to maintain their naval presence in the Syrian ports of Latakia and Tartous, the only Mediterranean harbors to which they have access.

Allowing Assad’s repressive Alawite regime to survive after he goes would be a distasteful solution. But the reality is that with Syria, the only choices left are bad ones. This is the least-bad alternative.

(Vali Nasr is a Bloomberg View columnist, a professor of international politics at the Fletcher School of Law and Diplomacy at Tufts University and a senior fellow in foreign policy at the Brookings Institution. The opinions expressed are his own.)

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To contact the writer of this article: Vali Nasr at vali.nasr@tufts.edu.

To contact the editor responsible for this article: Lisa Beyer at lbeyer3@bloomberg.net.