It's a matter of timing, and the numbers don't add up. The US surge in Iraq did not by itself bring about an end to the country's civil war in 2006-2007 as Washington and the received wisdom have maintained.

A temporary troop increase and the adoption of civilian-friendly counterinsurgency (COIN) tactics were largely too little too late. The primary factor responsible for the decline in violence in Iraq was the culmination of the sectarian cleansing of Sunnis - principally in Baghdad, formerly a thoroughly mixed ethnic city since the advent of the republic in 1958 and through Saddam Hussein's rule - by the newly empowered Shia majority in their drive to national pre-eminence.

The details of our argument are outlined in two reports available online: "Baghdad Night " (UCLA) and "Baghdad Divided"  (ISN). The former uses light emissions at night by neighborhood, before, during and after the surge to track the effects of the violence in the capital and to make its case. It was the predominantly Sunni areas that were overwhelmingly most likely to darken; the Sunnis were either killed or ejected and shut off the lights in the process. The latter report contains maps chronicling the sectarian cleansing of Baghdad and its consequent division. (Maps developed by Dr. Michael Izady for Columbia University's School of International and Public Affairs (SIPA) Gulf/2000 Project).

To begin, the sectarian cleansing of Sunnis peaked well before (December 2006-January 2007) the full onset of surge operations in mid June 2007 - as shown by data provided by the US Department of Defense, particularly the report issued by Gen. James Jones in September 2007, now President Barack Obama's national security adviser. Our light signatures and sectarian maps corroborate the effective partitioning of Baghdad by February-March 2007.

With much of the Sunni population left fleeing toward Anbar province, Syria and Jordan, and the remainder holed up in the last Sunni stronghold neighborhoods in western Baghdad and parts of Adhamiyya in eastern Baghdad, the impetus for the bloodletting waned. The Shia had won, hands down, and the fight was over.

US forces never had control over the contest. The extra boots served as a psychological boost to the American public and the Iraqi government. Their sole achievement on the ground was to seal off the newly segregated neighborhoods from one another, preventing the massacre of the remaining Sunnis in Baghdad, and finally, to nudge any still active Shia militia groups to back down.

The Sunni "awakening" component of the surge has also earned plaudits in decision-making and analytical circles for contributing to the cessation of hostilities. Surge backers claim that the Awakening Councils teamed up with US forces in their shared contempt for al-Qaeda in Iraq's (AQI) brutality, the outfit's burgeoning challenge to the traditional authority of the Sunni sheiks, AQI's role in igniting the civil war with the bombing of the al-Askaria shrine in the city of Samarra in February 2006 that the Sunnis knew they could not win, Sunni-AQI ideological rifts and the Sunni sheiks' search for a post-Saddam patron. This account, however, is incomplete.

There would have been an internal political price to pay by the Sunni sheiks for cooperating with the invading forces that had just toppled their ruling establishment; a cost likely much higher than tolerating the presence of AQI on their territory, a largely Sunni organization. Moreover, once on the US side, their fate would, in so many words, be in Washington's hands.

Rather, the Awakening Councils awoke and turned against AQI for an added and largely unreported reason: By the autumn of 2006, the Sunnis were looking down an exceedingly dark tunnel. They "awakened" to the prospect of total subjugation, if not annihilation, at the hands of the Shia.

When then-president George W. Bush announced the surge on 10 January 2007, he sent the Sunnis a signal: Get on board now and we'll guarantee your security and a modicum of political participation ... at least until we leave. Otherwise, continue fighting and risk extermination. They made the rational choice.

A charitable interpretation would have it that Washington's narrative overlooks the near wholesale sectarian cleansing of Baghdad that it indirectly triggered.

Iraq is now largely stable, at least as regards the Shia-Sunni conflict in Baghdad. The Shia are at the helm and the remaining Sunnis, a shadow of their former self, will likely acquiesce to majority rule, especially once the US leaves and the petrodollars start rolling in.

The US surge in Iraq did not play out as advertised. Rather, it fit into a series of converging and violent dynamics on the ground, coinciding expediently with a shift in the balance of power. That is what the empirical evidence shows.

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