It's mid-September, and I'm in Fallujah once again.  For four years, I've been visiting the same set of angry towns and sniper-infested farmlands in Iraq. On this trip, I stayed with 20 US and Iraqi units scattered across Baghdad and Anbar Province. In previous writings I have criticized strategic decisions, such as the administration's order in 2004 to seize Fallujah, only to call off the attack when Iraqi politicians complained. That fecklessness galvanized the Sunni resistance.

No combat veteran, however, can walk the streets without armor in tough cities like Fallujah today without recognizing that a sea change has occurred. People wave, shops are open, tips about insurgents pour in, residents turn in roadside explosives and the number of shootings has plummeted.

Yet many Americans want our troops to leave immediately. Why? Because many subscribe to the Top Down view of history that leaders shape the destinies of their countries. According to this view, because officials in Baghdad are fractious, frequently corrupt and incompetent, Iraq will founder, no matter what happens on the ground. Progress on the battlefields is discounted because the top Sunni and Shiites have not reached agreements.

An alternate view holds that the influence of leaders in shaping the course of nations is exaggerated, as Tolstoy demonstrated in his portrayal of Napoleon in War and Peace. Successful leaders ride groundswells caused by the desires and actions of millions of people. According to this Bottom-Up model, mass popular movements determine the flow of history.

The Sunni-based insurgency, for instance, sprang from the bottom-up. But beginning in the fall of 2006, the Sunni community, led by the tribes in Anbar Province, turned against al Qaeda because it had inflicted a Robespierre-like reign of terror. All 23 tribes in Anbar, the heart of the Sunni insurgency, have turned against al Qaeda, a shift predicted by no one a year ago. The Sunnis have accepted they cannot regain control.

On the other hand, the Shiite-dominated government is reluctant to share the power American sacrifices gave to them. Elements of the Jesh al Mahdi (JAM) militia control large swaths of Baghdad, intent on driving all Sunnis from the city. The Shiite police are incapable and untrustworthy. Only by deploying US and Iraqi soldiers into every district did General Petraeus curb the killings.

Hence the American military must pull off the trifecta of defeating al Qaeda in Iraq, building a competent Iraqi army and neutralizing rogue Shiite militias. Our military is on its way to delivering two winning tickets - defeating al Qaeda and building an Iraqi army.

That still leaves the militias. To push America out of Iraq, Iran is equipping JAM gangs to kill Americans. Our goal should be to inflict pain on both the gangs and on Iran in order to break the clandestine links causing the deaths of Americans. Maliki permits American raids to prune the militias, but hasn't allowed the Iraqi Army to systematically break the JAM organization. For fear of killers on both sides, for years to come Shiites and Sunnis won't be able to openly enter each other's neighborhoods. Each neighborhood must be protected separately. Permitting armed Sunnis to guard their own neighborhoods as legitimate police, backed by Iraqi Army units, is the tactical means of deterring the JAM death squads that operate as small gangs.

Over the long term (say, five years), an Iraqi Army with American advisers cannot co-exist with Shiite militias advised by Iran. The eventual dissolution of the militias, however, is an Iraqi, not an American mission. With a sectarian central government, Iraq has not emerged as a bastion of liberalism in the Middle East. We have no obligation to keep major American units there until it does. We should settle for a federal Iraq not aligned with Iran and able to defeat internal enemies, with oil revenues disbursed to de facto segregated provinces and Baghdad neighborhoods. The bottom-up trends toward those limited objectives are encouraging - if we are willing to station about 80,000 Americans for three to five years in advisory, support and combat backup roles.

Militarily, it makes no sense to stop now. Let our troops complete their two primary missions. The first is the counterinsurgency strategy to turn the Sunnis against the insurgent extremists. That is working.

The second is the destruction of the extremists. America's mortal enemy is al Qaeda, a transnational pathology. Our invasion in 2003 gave rise to an al Qaeda franchise in Iraq, mostly Iraqis who leveraged the resentment of their fellow Sunnis and then ruled by murder. Al Qaeda's Sunni base in Iraq has now turned against it. Put al Qaeda's disciples in the earth and scorn them. That will deal a heavy blow to its global mystique. Then, having prevailed, bring most of our combat units home over the next 18 months.