Another factor is that, as a result of the past two years' ethnic cleansing, much of Iraq, especially Baghdad, is now Balkanized. Sunnis have killed or chased away most Shiites in Sunni areas, and vice versa.
However, there are still vast swaths of mixed neighborhoods throughout Iraq, especially in Baghdad. And it is widely and firmly believed—by military commanders and seasoned reporters on the ground—that these areas would erupt in horrendous bloodshed if American troops were not clamping down on the fault lines.
Now here's the problem: All these phenomena—the surge, the alliances of convenience, the moratorium—cannot last forever. In fact, they can't last much longer than (pardon the phrase) the next six months, maybe (let's make it two F.U.s) the next year.
First, the troops. Not only will five of the current 20 brigades be out of Iraq by July, but Secretary of Defense Robert Gates and the Army chiefs would like to cut troop-deployment terms from 15 months back to their normal 12 months (with 12 months back home for rest and further training). The 15-month terms were always seen as a temporary measure. Talk to soldiers, and they will tell you that 15 months of continuous combat duty is simply too wearing. Enlistment rates are down; junior officers are dropping out at rates unseen since Vietnam days. The war in Iraq is the main reason for both trends. The Army is already stretched to the bone. Senior officers—and Gates—are deeply worried that maintaining this breakneck pace for much longer might break the all-volunteer Army.
However, if the terms of duty are cut back to 12 months of deployment, followed by 12 months home, it is not clear whether even 15 brigades can be sustained in Iraq for very long. And once troop levels fall below 15 brigades, it is not clear—as they approach 10 brigades, it is very unlikely—that the mission of securing the Iraqi population (the essence of counterinsurgency) can be sustained.
The clock is also ticking on the other games that are keeping ultraviolence at bay. After the Sunni-U.S. alliances defeat the jihadists, or reduce their ranks to a manageable level, nobody expects the Sunni fighters—who, before their "awakening," spent much of their time shooting and blowing up American soldiers—to become pliant citizens. (Stalin didn't join NATO or the IMF after he and the Western allies beat Hitler, either.) They will go back to shooting our soldiers, undermining the Shiite-led Iraqi government, or both; in fact, having gained the experience of fighting alongside U.S. troops, and the armaments that went with it, they will be a more formidable force in sectarian battles with Shiites.
If the Sunni insurgents resume their sectarian battles, it is doubtful that Sadr's Mahdi Army will maintain its cease-fire.
In sum, U.S. forces may soon have more eruptions to damp down—or, to switch metaphors, more holes in the Iraqi dike to plug up. And the task will be more daunting still once the troop-levels decline.
All this is why Gen. Petraeus and most other officers refrain from wild cheering at the reports of declining casualties and violence. They are pleased with the results; they have done what they set out to do, more creatively and successfully than many critics had predicted (and, I confess, I count myself among that number, too). However, they know, first, that these trends can be reversed in a flash and, second, that they mark only tactical successes in this sort of struggle—that the true, strategic signposts of success are, ultimately, beyond their control.
And that's why, this time around, the next six months might really be crucial.