Iraq for most Americans is now a toxic subject — best either ignored or largely evoked to blame someone for something in the past.

Any visitor to Iraq can see that the American military cannot be defeated there, but also is puzzled over exactly how we could win — victory being defined as fostering a stable Iraqi constitutional state analogous to, say, Turkey.

But war is never static. Over the last 90 days, there has been newfound optimism, as Iraqis are at last stepping forward to help Americans secure their country.

I spent last week touring outlying areas of Baghdad and American forward operating bases in Anbar and Diyala provinces, talking to Army and Marine combat teams and listening to Iraqi provincial and security officials.

Whether in various suburbs of Baghdad, or in Baqubah, Ramadi or Taji, there is a familiar narrative of vastly reduced violence. Until recently, the Americans could not find enough interpreters, were rarely warned about land mines and had little support from Iraqi security forces.

But now they are being asked by Iraqis in the Sunni Triangle to join them to defeat the very terrorists the locals once championed. Anbar, a province that just months ago was deemed lost by a U.S. military intelligence report, is now in open revolt against al-Qaida.

Why the change?

Officers offered a number of theories. The surge of American troops, and Gen. David Petraeus' risky tactics of going after the terrorists within their enclaves, have put al-Qaida on the run. Likewise, in the past four years, the U.S. military has killed thousands of these terrorists and depleted their ranks.

Sunnis — angry over their loss of power to the historically discriminated-against Shiites — discovered their al-Qaida allies to be worse than their Shiite rivals. We forget that jihadists drew in not merely religious fanatics but also repulsive common criminals and psychopaths who extort, butcher and mutilate innocents.

Iraqis of all tribes and sects are also growing tired of the nihilistic violence that is squandering the opportunity for something better than Saddam's rule. The astronomical spike in oil prices has resulted in windfall profits of billions of dollars for the Iraqi government — and with it the realization that Iraq could someday become a wealthy advanced state.

Iraqis told me that their widely held fear that Americans are going to leave soon has galvanized Sunnis to finally step up to secure their country or face even worse chaos in our absence.

The result is that ordinary Iraqis are increasingly willing to participate in local government and civil defense. Such popular engagement from the bottom up offers more hope than the old 2003 idea that a democratically elected government could simply mandate reform top down from their enclaves in the Green Zone.

So we are at yet another turning point in the constantly changing saga of Iraq. On this recent trip to Iraq, I rode on highways that just a few months ago were nearly impossible to navigate without being blown up by improvised explosive devices. Soldiers now train Iraqi security forces as often as they fight terrorists.

But there is also a new sense of urgency on the part of the military that Iraqis must seize this new opportunity before it fades. Unless the Shiite-dominated Iraqi government steps up to reconcile with the Sunni provinces and begins funding social services, the insurgency will only rekindle.

The Iraqi army must be freed up to police its porous borders with Iran and Syria. That's impossible without a national police force inside Iraq's cities that is both competent and law-abiding. So far the police are not quite either.

The Shiite community must appreciate that it has won the political struggle and finally achieved political power commensurate with its numbers. This majority must now take on Shiite death squads and their sympathizers inside the Iraqi government. Otherwise, an intolerant Shiite-run Iraq will either become a pawn of Iran or fight a perpetual war with the country's Sunni provinces.

Meanwhile, the American military, after four years of hard fighting in Iraq, is strained, its equipment wearing out. America's finest citizens, fighting for an idealistic cause that has still not been well explained to the American people, continue to be killed by horrific murderers.

If the unexpectedly good news about the surge has given Gen. Petraeus another six months to improve further the situation, the political debate at home has changed only from "Get out now!" to "Victory still isn't worth the cost in blood and treasure."

Lost in all this confusion over Iraq is the fact that about 160,000 gifted American soldiers are trying to help rebuild an entire civilization socially, politically and economically — and defeat killers in their midst who will murder far beyond Iraq if not stopped.

Victor Davis Hanson is a classicist and historian at the Hoover Institution at Stanford University. Reach him at author@victorhanson.com.