To date what lessons have been learned about the allied invasion of Iraq? What might be its legacy and impact on future conflicts? From the perspective of one year later, here are the assessments of Washington Post Pentagon correspondent Thomas E. Ricks, New York Times correspondent Todd Purdum, Atlantic correspondent James Fallows, former Secretary of the Army Thomas White, Lt. Gen. James Conway, and military historian Frederick W. Kagan. Their comments are drawn from their full interviews with FRONTLINE.

Secretary of the Army, 2001-2003.

For you, what were the key lessons learned from this war?

A, In the world that we face, the combat phase may be the easiest part; B, that what follows the combat phase is where most of the strategic objectives will be achieved or not achieved and, therefore, it deserves as much planning and attention as the combat phase does. Three, until you've done that, don't start the operation in the first place. Fourth, it's going to take you a long time and a great deal of effort if you get into anything the scale that we've gotten into in Iraq. So you'd better be ready for it.

Are you personally angry about the way the postwar's been mishandled?

I think we should all be angry. It is ultimately going to cost an enormous amount of treasure, and how many lives, I don't know. But certainly the burden to the country is going to go on for a long time. I don't think we adequately addressed that on the front end.

Is the world a better place because Saddam is gone? Certainly. Will Iraq eventually become a better place for the average Iraqi on the street? Certainly, we hope it will. But it isn't yet, and we've got a long ways to go.

Commander of the U. S. Marine Expeditionary Force in Iraq

How valid is it to draw lessons from this conflict? ...

... I think we'd better be careful drawing lessons from the whole of the effort, if you will. I'd have cautioned our headquarters and our decision-makers that this is probably an anomaly, both for the Marine Corps and perhaps for the nation. ... I also think that we should not formulate changes to the force structure based on what has now been a couple of fights against Iraqis. I don't think [they had a] terribly efficient army. I think both the Gulf War and this Operation Iraqi Freedom will show us that. …

So the light footprint has worked in Iraq, [but] it wouldn't necessarily work elsewhere?

The footprint needs to be determined by each situation, and I think that a competent set of planners would give us that. There might be a situation similar to this, but with different forces defending, [in which] what we impose wouldn't work at all. …

But for the people above you -- would your message be [to not] always think it'll be this easy?

Yeah. … Again, we've just got to make sure that we put the right force against the right requirement, wherever that may be. We've got the force to do it. You can say that two divisions defeated the Iraqi Army in this case, because that's essentially what it boiled down to -- very well supported, of course, by carrier air, the Air Force. But two ground divisions essentially moved up to Baghdad. ...

Pentagon correspondent for The Washington Post.

There are tensions still at the Pentagon [between the uniformed military and the leadership]. What strikes me is the degree to which [the uniformed military has] been suppressed, and which officers have been told, "You will not voice dissent," -- to the point that they don't even need to be told that anymore. They just know, "You don't voice dissent around here."

But the Army, to its credit, still keeps on poking its head up. Just about three weeks ago, the Army War College issued a very scathing study by a visiting professor that denounced the Bush administration's conduct of the entire war on terrorism, and especially its approach to Iraq. So the Army still was kind of saying, "No, we're going to be professional, and give our best opinion, even if it disagrees with the administration."

Lastly, knowing the antagonism that exists between the Pentagon leadership -- Rumsfeld, Wolfowitz-- and the uniformed military, what happens in the next war that comes?

I think it's impossible to predict exactly how it plays out. It depends on who the civilian leadership is, what the lessons that the military -- and especially the Army -- ultimately draw from Iraq.

Iraq's an open question; we don't know how it's going to end. We don't know how this will be viewed 20 years down the road. Will this be seen as a Vietnam-scale mess? Probably not. Will it be seen as somewhat like the U.S. intervention in the Philippines at the turn of the century? Could be.

But an interesting side effect of all this is that you basically have the most combat-seasoned, combat-experienced Army that this country has had in decades. Most people in the U.S. Army are either in Iraq now, or have been in Iraq, or are getting ready to go to Iraq. A lot of those people have already been in Afghanistan. A lot of them also have been in Bosnia, Kosovo, or even the 1991 war. They're going to have a lot of credibility when they talk to the American people, and they talk to Congress -- probably more credibility than civilian leadership will have, no matter who the civilian leadership is.

What might that mean?

What it might mean is, despite the image a lot of people have of the military as eager to go to war, the military is actually quite eloquent in arguing against going to war, in arguing for other tools to be used, especially diplomacy. I think what you'll see is a lot of military officers saying, "Before you go to war next time, try some other tools. Try diplomacy. Get better intelligence. Don't stick it all on us."

Military Historian

War is not about breaking things and killing people. Battle is about breaking things and killing people. War is about achieving a particular political end state. The "killing people and breaking things" part of that is subordinated to that end state. If you're going to achieve that end state, you're going to have to do more than break the right things and kill the right people.

You're certainly going to have to use diplomacy. You're probably going to have to engage in stability and support operations of various varieties. You're going to have to interact with the local population in various different ways. You're going to be in a much more complicated environment than one in which you simply have targets and the weapons systems that attack them.

Unfortunately, our current military doctrine is moving very much in the direction of seeing all potential enemies as target sets, and not seeing them as collections of human beings with weapons, where what really matters is your interaction with the human beings. Your interaction with the weapons systems has to be subordinated to that.

There have been mistakes made. What should be done now to make up, to some extent, for the mistakes in the past?

It's an incredibly hard question. We've gone down a very dangerous road. The most urgent thing that we have to do now is suppress the insurgency. If we turn over to an Iraqi government in a few months' time a state in which there is significant ongoing insurgency, I think the likelihood of the success of that government is very low.

It's time to open the coffers. It's time to spend all of the reconstruction money that we have, a lot of which isn't being spent. It's time to make clear to the Iraqis that we are committed to their long-term well being and that we're interested in doing more in Iraq than simply chasing Al Qaeda, and really to show them that what's important here is their future, and not our past interaction with Saddam and our concerns with Al Qaeda.

We have not been very successful at getting that message out to them, and I think there have been a lot of bureaucratic reasons for that. Time is running out to solve that bureaucratic logjam and make this work. But on the other hand, good things have been happening, and we might be able to build on them.

But above all, it's time for the real Iraq Marshall Plan. If we think for a minute about how significant a democratic regime in Iraq would be throughout the entire Muslim world, how that would transform the debate in the Muslim world about what choices to make and who to support and what to do, and how disastrous it would be if we try to set up a democratic Iraqi regime and have it destroyed by Islamist insurgents.

What price would you like to pay? I mean, there's hardly any price you could pay that would be too high to achieve the aim and avoid the disaster. I just think we've been going at this in a very parsimonious fashion, trying to restrict our commitment, and that's just not the way to do it. It's not the way we did it in Germany. It's not the way we did it in Japan. And it's not the way we should be doing it here.

New York Times correspondent and author of A Time of our Choosing, a comprehensive account of the invasion of Iraq.

Clearly, in purely military terms, the invasion succeeded on the grounds it set for itself. It was a swift and surprising advance that toppled a regime that turned out to be weaker than we even thought.

In political and diplomatic terms, it was a much more mixed bag. The invasion had strained alliances with Europe; strained America's involvement with the United Nations and the broader world community; raised all sorts of new questions about whether it had really created a Middle East that was more congenial to American interests; whether Americans would be safer; whether the Israeli-Palestinian peace process would be helped or hurt; how the Muslim world would regard America; how countries all over the world would regard the use of American power.

Those questions are still unresolved, and will be for years.

How did we end up with an easy war and a messy peace?

Oh, the peace is always harder. I think most generals are quick to say that, and there's no doubt that America is the supreme military power of the world. It stands unchallenged with equipment, manpower, resources, resolve. Being strongest doesn't mean being smartest always, and the hard work of the peace is the most grinding challenge that war makers ever face.

…There's no doubt that Rumsfeld and Franks's plan succeeded militarily. It did what it was supposed to do. There also seems to be no doubt that postwar occupation of Baghdad was not what it should have been, either because we didn't have enough troops, we didn't have enough planning. We planned for the wrong things [and] the Pentagon had a certain degree of arrogance in forcing the State Department out of the planning at an early stage.

It will remain one of the most tantalizing, troubling questions about this war -- whether it turned out to be a tactical victory with strategic disappointments because the thinking was not what it should have been.

National correspondent for The Atlantic magazine.

As a strategic decision about how to deploy U.S. force, in the largest sense, I think the campaign as a whole will be studied for its failures. The U.S. incurred foreseeable preventable errors and mistakes in the weeks and months after that brilliant military campaign. So it was a brilliant tactical success that was part of a strategic failure. The United States can still -- and must still -- see its way through to some kind of successful outcome in Iraq. But the task is much, much harder for the United States and for the Iraqis, because of the preventable errors the United States made after the war.

Explain to me how that is possible. We went into this war, not simply to fight the war, but we were going in there to change the Middle East, to some extent, to set up a second democracy, after Israel. Wouldn't it have been normal to have understood that what happened postwar was just as important as what happened during the war?

I would have thought that the people who, number one, cared most about removing Saddam Hussein and his threat, and number two, cared most about making Iraq an example of democracy to the Arab Islamic world, would have been the most insistent on taking the long view -- on making sure the whole campaign was a success, not just the military campaign to take over Baghdad.

So it is a mystery to me, even now, and something that I think will take years for scholars to really explain -- how those same people could have been so indifferent about the postwar consequences in Iraq.