U.S. military officials say violence is dropping around Mosul, where insurgents have for months escalated attacks. In January, U.S. military data show there were more than 500 attacks across Ninewa Province, where Mosul is the largest and most volatile city by far. A senior military official speaking on condition of anonymity said the attacks in the province in February were expected to total roughly 400.

Even if the projections bear out, Mosul still remains a vicious battleground for Iraq, which has seen overall violence fall dramatically in recent months in the wake of the surge. And the city of 1.8 million people continues to vex U.S. military leaders, who have watched its troubles ebb and flow over the years.

In late 2003, Mosul was largely peaceful by comparison with the rest of Iraq at the time. The burgeoning insurgency, then beginning to spread across other areas of Iraq, was slower to take hold in Mosul for a number of factors. Mosul drew a measure of stability from its history as place of relative wealth and sophistication, whereas early insurgent havens like Fallujah and Ramadi were poor, troubled places even under Saddam Hussein. And some leaders among Mosul's Sunni community for a time held out hope of finding a role in the emerging post-invasion power structures even when Sunnis elsewhere were quickly adopting a rejectionist mentality. General David Petraeus, who was then head of U.S. forces in northern Iraq, says Mosul's first real plunge into violence came in 2004, after he handed over command of the area. The police force collapsed, and insurgents moved in. "Once the roots go in, then you have a real challenge," Petraeus says of the insurgency. "You just start to spiral downward."

In the years afterward, violence in Mosul fluctuated as insurgents kept up a presence in the city. But the situation there seemed much more stable than many parts of Iraq such as Baghdad and Ramadi. Then in 2007, as surge forces began reducing violence across Iraq, the picture in Mosul worsened, leaving it the only place in the country where violence was rising as the year closed. Iraqi and American officials agree that Mosul is now probably the last urban stronghold of the insurgency. Iraqi Prime Minister Nouri al-Maliki dispatched additional Iraqi army troopers to the area, promising a "decisive battle" that has yet to materialize. But in any case Petraeus and other U.S. commanders believe that efforts to fix Mosul this time are destined to work better, chiefly because nationalist Sunni fighters are rethinking their alliances with al-Qaeda in Iraq and, in some cases, becoming open to reconciliation.

"Sunni Arabs have evolved," Petraeus says. "They realize that al-Qaeda has brought them nothing but indiscriminate violence and bloodshed and in many cases oppressive practices such as forced marriages. And in some cases bizarre practices such as breaking fingers of people who smoke."

The military strategy in Mosul for both U.S. troops and Iraqi security forces is much the same approach used elsewhere in Iraq over the years, with mixed results. Absent, however, is one key aspect that shaped progress in other places over the past year: local volunteer security forces who, in many cases, were nationalist insurgents who broke with al-Qaeda in Iraq. U.S. officials say that strategy won't work in Mosul, because standing up bands of irregulars could inflame existing ethnic and sectarian divisions in the city. So many U.S. military officials see provincial elections as a way to sap the insurgency's strength in Mosul. In the 2005 elections, many Sunnis across Iraq simply did not participate, a defiance that left them dejected and marginalized  and susceptible to the embrace of insurgent elements. Petraeus and other American officials in Baghdad think Sunnis will take part in elections this time and rejoin the civic process rather than rage against it. "They want their seats at the table back," Petraeus says.

Still, an opportunity for reconciliable Sunnis to turn from the insurgency to participation in the government does not appear to be near. Last week, Iraq's presidential council blocked a proposal for new provincial elections, sending the measure back to the parliament for reconsideration. So U.S. and Iraqi forces in Mosul are left to slog on against the insurgency rooted there without the prospect of a change in the political dynamic that might alter the situation in the way the tribal revolt in Anbar Province against al Qaeda in Iraq did last year.