If the results of one war could serve as a tutorial for the next -- if generals truly could fight the last war every time -- we could write one book on how to conduct military activities and be done with it. But we know the folly of that.

What's less known is that it's the same for pundits as it is for generals. Every conflict is different. It's the rare analogy that truly holds up, that truly illuminates.

Comparisons of Vietnam and Iraq, two wars that could not be more different, is a case in point. The military objective in Southeast Asia was to insure a free, independent South Vietnam. We failed. And we failed for a simple reason: We couldn't prevent the North Vietnamese army from invading the South. The military objective in Iraq was to overthrow the regime of Saddam Hussein. In this, we did not fail. He's in American custody. The war is over.

The mission that the U.S. military is performing in Iraq today differs significantly from its combat duties in Vietnam. The United States has legal and moral obligations as an occupying power -- establishing a legitimate government, fielding an Iraqi military and police and preventing widespread privation, sickness and disorder. These tasks are neither easy nor optional.

And the notion they can be accomplished without any violence or friction is fanciful. They call this the "post-war period" for a reason. There is still some war left. There are always those who refuse to give up fascist dreams or seek to disrupt reconstruction and perhaps seize power for themselves.

Defeating the enemies of peace, however, is different from crushing an opponent in war. It calls for a disciplined, measured use of force, and the right balance of political and military initiatives. It also requires a strategic eye. Success will be measured not by the number of terrorists and renegade militiamen Americans kill but by whether we establish a legitimate government, put Iraqis in charge of their own security, and let them take responsibility for their own future.

Yet, the fact that Baghdad is not Saigon, Beirut or Mogadishu doesn't mean we can't learn lessons from military history. And that history tells us success requires achievable policies, backed by sound strategies, and the will and resources to persevere.

In this respect, the war in Vietnam does offer a point to ponder -- the impact of the 1968 Tet Offensive. On Jan. 31 of that year, during the annual cease-fire to mark Tet, the traditional Vietnamese celebration of the Lunar New Year, the North Vietnamese Army launched a cross-border invasion timed with an uprising by Viet Cong insurgents in cities throughout the South.

The Tet Offensive proved a crushing military defeat for the North Vietnamese. The NVA endured a severe beating, and the Viet Cong insurgency was so decimated that it never truly emerged again as a serious military or political force.

But that's not how it played in the United States. Here, thanks to biased reporting and inaccurate first impressions, many thought American forces had suffered a catastrophic defeat. And as military expert Lewis Sorley explained in his book, "A Better War," this incorrect impression may have cost the South Vietnamese their country.

Around that time, the U.S. military had begun to turn over responsibility for ground defenses to the South Vietnamese, and they proved capable of defending their own country as long as they received material and firepower support equal to the aid the North was getting from the Soviet Union and China. But after Tet, little political will existed for continued support for the South on the political left or right. Neither a Nixon administration crippled by Watergate, nor a Ford presidency looking to find its footing in Washington could muster the votes to continue aid. It was then -- and only then -- that South Vietnam collapsed.

This is not an argument to mimic the military strategy the United States used in Vietman. It is an argument against wavering in our support for establishing a free, vibrant Iraq. What Vietnam taught us is that when one loses sight of the goal, things can go terribly wrong.

The goal in postwar Iraq is different than it was in Vietnam. Americans aren't trying to prevent an invasion in Iraq; they're trying to help the Iraqis establish and run their own government. This requires the administration to find a strategy that accomplishes the essential political and security tasks ahead. It requires the American people to continue to provide the resources and determination needed to meet our obligations.

If we let firefights in Fallujah and elsewhere distract us from the real work to be done, then we will be repeating the mistakes of Vietnam.