IN July, five American soldiers died in action in Iraq. That's the lowest number since the war began in March of 2003. A prudent leader, Gen. David Petraeus has warned his commanders not to claim success yet. Nonetheless, in traveling around the country in early August at Petraeus's invitation,

I found the progress on the military front to be remarkable. It was my 15th trip to Iraq in six years, and after the hard fighting I had witnessed in the past, the contrast was striking. That raises three questions: How did the war turn around? What are the current conditions? And where do we go from here?

In the spring of 2003, the United States quickly won control of Iraq from Saddam Hussein. Afterwards, however, it failed to prevent the growth of diverse insurgent forces. By 2004 most of the Sunni population from Baghdad west to the Syrian border and north to Mosul supported, or at least tolerated, resistance cells and Qaeda-led terrorists in their midst. The U.S. responded by cracking down, and its operations were rough enough to antagonize the Sunni population, even though it avoided the draconian restrictions that armies have historically employed to control populations. By the end of 2004, the U.S. was thinking about getting out.

The U.S. military settled on a mission of handing off the war to newly formed Iraqi-army battalions. Unfortunately, these battalions weren't up to the task, and they received no leadership from two successive governments that were inept and sectarian, having been elected from lists supported by the block vote of the Shiite majority. By the spring of 2006, the coalition was losing on the two major fronts that accounted for most of the fighting. In Anbar Province, to the west, the extremist Sunni al-Qaeda in Iraq controlled the population; in Baghdad, to the east, death squads drawn from the Shiite militias and the police were driving out the Sunnis, while al-Qaeda's suicide bombings continued. The situation was grim, and to those back home in America, it seemed destined to keep getting worse.

In fact, conditions were ripe for a turnaround. In the fall of 2006, tribal leaders on the western front (Anbar) turned against al-Qaeda. Back in 2004, the same tribes had welcomed al-Qaeda, with its stirring call to jihad. Anbar, it was then thought, would be the last province to be pacified, if it ever was. But that judgment didn't factor in a staffing policy that turned out to be enormously important: The Marines were sending the same battalions back to the same cities on seven-month tours.

Over the years, the Americans and Iraqis grew to know one another, and Marine tactics improved as they became familiar with the area and its people. The Marines did their best to keep the peace with small foot patrols as the population went through a cycle of opposing them (2004), resenting them (2005), and finally seeking their protection (2006) after experiencing al-Qaeda's rule. Like Robespierre in 1793, al-Qaeda had turned into a terror machine after seizing power.

The key to the turnaround on the western front was a strategy of partnership between local leaders and U.S. officers. Insurgencies grow from the bottom up; they must be defeated by turning the population against the rebels village by village, city by city. No general, no matter how brilliant, can accomplish this by maneuvering his army. Instead, the army and the police must spread out and remain among the population.

Outside the cities, the distances between the farmlands were so huge that Qaeda operatives could move freely. The Sunni tribes, however, under the remarkable leadership of Sheik Abu Risa Sattar, gradually united in rebellion against al-Qaeda. The locals knew who the extremists were; the Americans brought the hammer. After the tribes, now aligned with the Americans, had been successful in killing some Qaeda members, the bulk of the Sunni population joined with them. Al-Qaeda, whose mobility depended upon cars, couldn't move inside the cities where police checkpoints were improving, and couldn't hide in the countryside, where tribal posses were pursuing them. By the fall of 2006, similar local partnerships had sprung up across the west--in the cities of al-Qaim, Haditha, Ramadi, and even truculent Fallujah. The war in the west had turned before President Bush announced his surge strategy in January of 2007.

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When Petraeus took command in February 2007, he was impressed to see that thousands of Sunnis, many of them ex-resistance fighters, had joined tribal auxiliaries and the police in Anbar to oppose their former allies. He authorized U.S. commanders to recruit and pay similar irregular forces across Iraq. Al-Qaeda fled, Shiite death-squad attacks ceased, and a further benefit was that these partnerships placed Americans in daily contact with local leaders, who told them about poor services. In turn, the Americans pressured the Iraqi government to respond to local needs.

The turnaround on the eastern front--around Baghdad--followed in 2007. The same sorts of partnership emerged, shaped by three decisions at the top. First, President Bush sent a "surge" of 30,000 troops, mainly to control Baghdad. Second, their commander, Lt. Gen. Raymond Odierno, chose to deploy most of them in belts around the capital to crush al-Qaeda. Third, inside Baghdad, Petraeus moved his soldiers off their large bases and into neighborhoods, especially along the fault lines where Sunnis were being driven out or where al-Qaeda was in control.

In and around Baghdad, Petraeus's strategy of deploying American soldiers in largely Sunni locales had succeeded by the end of 2007. As had been true on the western and eastern fronts, the necessary antecedent was a change in attitude of the Sunni population after experiencing al-Qaeda's whip hand, which contrasted sharply with the Americans'much more humane approach. With informants coming forward in every neighborhood, al-Qaeda was squeezed out of province after province. Odierno kept expanding the population-protection coverage, driving al-Qaeda to make its last stand in the north around Mosul, where heavy-handed Kurdish influence had antagonized the Sunni population and provided a nesting ground for the hard-pressed al-Qaeda extremists.

Illustrative of the military progress was the situation in the Muhamadiya district, south of Baghdad, previously called the Triangle of Death. There, the 3rd Brigade of the 101st Air Assault Division, having recruited 20,000 Sunnis into the Sons of Iraq (a collection of neighborhood-watch groups paid modest amounts by the Americans), was partnered with the 17th Iraqi-army division. By mid-2008, conditions had so improved that Col. Dominic Caraccilo, the brigade commander, devised a plan to steadily reduce his presence from 15 infantry companies (three battalions) to five (one battalion). That's roughly one U.S. company per Iraqi brigade in a vast sector, which covered 500 square miles holding 150,000 Shiites and 450,000 Sunnis. The shrunken brigade would be called a "transition task force."

DIFFERENT TRIBES, DIFFERENT METHODS

But in Shiite areas under militia control--like Sadr City, which was run by the renegade preacher Moqtada alSadr and his Jaish al-Mahdi (Mahdi Army)--the situation was entirely different. Sadr's political coalition in the national assembly had delivered the critical votes to elect Maliki in April of 2006. Throughout the second half of 2006, Maliki prevented coalition troops from systematically attacking Shiite death squads, many belonging to the Mahdi Army. Then in May of 2007, Vice President Cheney flew to Baghdad to pressure Maliki. He responded by letting the coalition attack the Iranian-backed special groups within the Mahdi Army, which were killing Americans. But large areas inside Baghdad, like Sadr City, remained off-limits to a full-scale American presence due to both Maliki's reluctance and the American designation of al-Qaeda as the main focus of attention for U.S. forces.

For years the Jaish al-Mahdi had shaken down its fellow Shiites in Baghdad, Basra, and elsewhere. While the Sadr movement as an ideology offered hope to the poor and thus retained some appeal, the thuggish behavior of its leaders eventually deprived them of the population's respect. Petraeus largely left Sadrist areas to Iraqi prime minister Nouri al-Maliki to deal with, and at first this strategy did not accomplish much.

A partial turning point came in August of 2007, when the Mahdi Army, during a fight with rival Shiite factions, killed a group of Shiites on pilgrimage in Karbala. Maliki turned up the heat by leading an armored force into the city and personally arresting a top Sadrist. With his militia losing popular support, Sadr grandly declared a "ceasefire," as was his custom whenever threatened. Maliki emerged more powerful, but when the crisis passed, so did his zeal, and he relaxed the pressure against the militias.

Then, in late March of 2008, he changed course yet again. In a bizarre episode, Maliki himself directed a sudden attack against the Mahdi Army, which was entrenched in the key southern city of Basra. Arumor had circulated that a cabal of Shiite politicians was encouraging the Sadrists to launch rocket attacks against the Green Zone in Baghdad. This would demonstrate Maliki's weakness, whereupon the politicians would orchestrate a vote in the assembly to remove him from office.

Maliki's abrupt move against Sadr's stronghold in Basra angered and surprised the Americans. The offensive faltered due to lack of preparation as well as command confusion: "The Iraqi operations center," an American general told me, "consisted of Maliki with eight cell phones yelling at his generals in a separate building with four cell phones." Rather than let the offensive fail or drag out, Petraeus sent special forces, electronic and surveillance intelligence assets, and air controllers to help the Iraqi battalions. With airborne video capturing the movement, day or night, of anyone stepping outside with a weapon, and attack helicopters waiting to pounce, the overmatched Mahdi Army broke apart.

At the same time, guerrillas inside Sadr City were launching Iranian-supplied rockets at the homes of Iraqi politicians in the Green Zone. U.S. ambassador Ryan Crocker persuaded Shiite, Sunni, and Kurdish politicians to unite behind Maliki against what had become a common threat. Petraeus deployed American units alongside Iraqi battalions to occupy the rocket-launching points and wall off the southern portion of Sadr City.

As had happened in Basra, Mahdi Army elements became targets for American units expert in detecting movement, identifying those with weapons, and calculating the geometries of fire. Several hundred militia members were killed. The Sadrists learned once again, as they had during similar battles in 2004, that challenging Americans to an open gunfight was not a prudent tactic. The Mahdi leaders fled, and Maliki sent Iraqi battalions to occupy Sadr City, without American units.

By the summer of 2008, the military situation had improved dramatically. Ambassador Crocker cited what he called "a virtuous cycle": The Shiites had seen the Sunnis turn against al-Qaeda, and the Sunnis had seen Maliki and the Iraqi army turn against Sadr's militia. In both cases, the desire for peace and freedom had overcome factionalism.

Al-Qaeda in Iraq had been attrited from about 4,000 to 2,000 and driven from most parts of the country. The much larger Sunni resistance movement, composed of dozens of small, independent cells, had largely collapsed. The Sunni tribes had allied with the Americans, though they still expressed distrust and hostility toward what they called "Maliki's Iranian government" for its perceived pro-Shiite bias. About 100,000 Sons of Iraq had been recruited across the country; each was paid about $300 a month from American military funds. Meanwhile, the Shiite extremists in the Mahdi Army were isolated, with about 500 receiving terror training in Iran from Iranian and Hezbollah specialists. The bulk of the Mahdi Army was leaderless, with the quixotic Sadr playing computer games in Iran, and the Shiite population wanted no more of his greedy, brutal toughs.

IRAQ TODAY

While the situation in Iraq has improved greatly over the last two years, many challenges remain, both military and political. On the military side, the relationship between the Iraqi army and the police is fractious in some locales and acceptable in others. The leadership of the national police, a disgraced organization that was complicit in killing Sunnis two years ago, has been replaced, and recent assessments have been positive. In theory, Iraqi-army battalions are supposed to withdraw from the cities as the police demonstrate competence. In practice, a combination of politics, distrust, and factionalism indicates that it will be years before the balance between the police and the military is resolved. Maliki, in a move to centralize power in his hands, is pushing for provincial operations centers that will include police and military commanders, both reporting to him.

Levels of capability and confidence vary from one Iraqi division to another, but overall, the Iraqi army is in no rush to see the U.S. units depart. The battles against forces aligned with al-Qaeda in the northern provinces of Diyala and Nineveh, including Mosul, are far from finished. In Diyala, too much civil power resides in the hands of Shiite officials who continue to repress the Sunnis. In Nineveh, the provincial government is terribly led and the Kurds have been unwilling to share power equitably with the Sunnis. Those provinces are a year to 18 months away from sustainable security without an American combat presence.

Out west in Anbar Province, long the stronghold of the Sunni resistance, the anti-Qaeda "Awakening" of the tribes has blossomed into a political party that opposes both Maliki's administration and the Iraqi Islamic party, a Sunni organization elected in 2005 when most Sunnis boycotted elections. (The IIP is part of Maliki's governing coalition.) The tribes, confident of winning the next provincial election, accuse the IIP of theft on a grand scale.

The Sunni tribes insist that a continued U.S. presence is indispensable. As Sheik Ali Hatim of the Jabouri tribe put it, "Everything we have--fuel, schools, salaries--is because of the Americans. We told Senator Obama, 'Don't pull out the Americans.' Without them, we will fight." According to Sheik Hatim, in his tribal area around Ramadi, 477 Iraqis in the last two years have confessed to working for al-Qaeda. He didn't say what happened to them.

Petraeus describes the recent military gains as fragile. Colin Powell once explained the U.S. situation in Iraq with the analogy of breaking a vase at Pottery Barn and thus being charged for it. The Iraqi army is the glue that has stuck the vase back together. The American military is the tape around the vase that must be carefully peeled away after the glue sets. If the tape is ripped away too quickly, the vase will fall apart again.

Given the progress on the military front, politics--working out who gets what without resorting to violence--has emerged as the main area of effort for the U.S. Provincial elections were supposed to be held by the end of 2008, but the assembly failed to pass an election law when it could not reach a compromise with Kurdish leaders about the status of Kirkuk. The assembly will try again in the fall, but many Shiite and Sunni representatives, having failed for two years to deliver basic services, will want to delay an election that could throw them out of power.

Meanwhile, Prime Minister Maliki has been steadily amassing power in the central government (meaning his immediate office). Maliki is notoriously overconfident. For two years, President Bush reassured him with video-phone calls every few weeks. This undercut the clout of Ambassador Crocker, because Maliki could claim to listen to no one except the president of the United States, who treated him as an equal. Maliki has also bumptiously discounted the American military role in staving off serious setbacks in Basra and in Sadr City, wrongly believing he can keep the security situation under control with the Iraqi army under his thumb.

Maliki is also sectarian. Deeply distrustful of the Sunnis, he has seen no reason to bring even a modest portion of the Sons of Iraq (some of whom have Qaeda involvement in their past) into the security forces. For over a year, Petraeus has been trying to persuade Maliki to accept at least 20,000 SOI members into the police and army, but Maliki refuses to consider it. Recently, to the Americans' distress, he has moved to arrested SOI and Awakening leaders.

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THE WAY AHEAD

The first major hurdle lying ahead will be negotiating a status-of-forces agreement (SOFA) between the U.S. and Iraq. This will take effect when the current U.N. charter, which authorizes the coalition's presence and use of force, expires at the end of this year. Maliki is insisting on very tough terms, including transfer of about 15,000 prisoners to Iraqi control (which could expose Sunnis to undue harm and possibly lead to Shiites being improperly released) and advance notice and coordination with Iraqi-government officials before launching operations (which will result in leaks and long delays).

The most extreme demand--that U.S. soldiers be subject to Iraqi laws and prosecution--will be rejected. But Maliki is also insisting on timelines, such as the withdrawal of U.S. combat troops from urban areas by 2010. Whatever the final details, it is certain that Maliki will insist on a SOFA that reduces American leverage and hastens the exit of other members of the coalition, who will be reluctant to enter tedious discussions with Iraqi negotiators who don't care whether they stay or go.

On September 16, Petraeus moves up from his current job as commander of Multi-National Force-Iraq to take over U.S. Central Command, where he will recommend how to balance forces between Iraq and Afghanistan. Petraeus's former deputy, Gen. Raymond Odierno, is taking over in Iraq. This will be his third tour in that country. The next U.S. president will inherit a stable but fragile military situation in Iraq.

The major challenge will be political, with both provincial and national elections--including the post of prime minister--looming. The question that Stephen Hadley, President Bush's national-security adviser, raised in a memo in November 2006 still applies: "We need to determine if Prime Minister Maliki is both willing and able to rise above the sectarian agendas being promoted by others. Do we and Prime Minister Maliki share the same vision for Iraq?"

If Iraqis believe America is abandoning them, their nation will fall apart. Our involvement in Vietnam ended in 1975 when the last helicopter flew out of Saigon, leaving behind a panic-stricken mob at the mercy of their conquerors. Alternatively, the endgame can occur when things quiet down enough that the press places Iraq on the back pages, as it is now doing. If Iraqis believe America is standing by them, they will hold together and the violence will continue to abate as our forces gradually leave.

Some American forces will be needed for years, in steadily decreasing numbers. Senator Obama's pledge to remove all combat brigades within 16 months, first made when a civil war was raging two years ago, is not relevant to today's circumstances; the definition of "combat" is too elastic to be relevant. The model shown by Colonel Caraccilo, in which a brigade of three battalions is gradually reduced to a single-battalion transition task force, is likely to be widely duplicated.

Wars turn on confidence. Iraqis--soldiers, police, and citizens--need to believe that Americans will aid them in extremis, though that need will diminish as the Iraqis learn to stand on their own feet. To use Petraeus's phrase, the definition of victory is "a sustainable security arrangement ... that Iraqis can take over by themselves."

Maintaining and reinforcing a stable Iraq is in the economic and security interests of the United States. We can and should gradually withdraw most of our troops; the Iraqi politicians will see to that in any event. And as we do so, we must continue to reassure the Iraqis that we stand beside them.

The burden and pain of Iraq were borne by a relatively small number, like Jim and Maria Simpson, who lost their son Abe, as well as Abe's best friend and cousin, Jonathan. Both died fighting in the Habbaniyah-Fallujah corridor. "Just a few families stepped forward," Jim Simpson told me. "I think we're losing the sense of being a nation." Losing the sense of being a nation should concern us all. We have fought the war in Iraq as a nation divided. If we are still this divided in the next war, there is a good chance we will be defeated.

Public support will be the key to any future conflict. Wars are strewn with blunders, and mistakes are not a reason to abandon the mission. Yet as the American military has adapted continually to overcome its mistakes and those of the government, American society has became more divided. As Rome and Athens demonstrated two millennia ago, every military, no matter how strong its internal code, eventually mirrors its society. It was easy to criticize the Bush administration for its faults; it is harder to decide how our society can retain sufficient unity to be the world's strongest tribe.

Mr. West is a former assistant secretary of defense and Marine. His third book on Iraq is entitled The Strongest Tribe: War, Politics and the Endgame in Iraq.