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President Obama’s speech tonight announcing the end of combat activities in Iraq will be greeted with a national sigh of relief rather than a flag-waving hurrah. And it is driven more by Election Day 2010 than the Iraq-U.S. mandated withdrawal date of December 2011.

Editor’s Note: Watch the president’s speech tonight on Fox News Channel at 8 p.m. ET.

But putting aside politics and public opinion, let's turn to the military realities on the ground. It is an ironclad rule of the American armed forces that immediately after a military engagement, those involved write something call an “After Action Review (AAR),” analyzing what happened, why it happened, and how it can be done better. If it's a thorough AAR, it concludes with a section on the “lessons learned.”

So how should we write the AAR on the Iraq War? The maddening thing is, we can’t. It’s not over. The U.S. combat phase may be ending, but we’re not sure the war is over. Some well respected experts argue that it’s far too soon for U.S. forces to leave, the Iraqis aren’t ready and the country will once again descend into chaos and civil war; that our politically driven withdrawal means we will snatch defeat from the jaws of victory.

Other, equally respected experts argue that it’s time to take the training wheels off the bike. The Iraqis are ready to ride, even if the bike is a little wobbly at first. And, just in case, we are keeping enough American troops in country to help with the steering.

Others say enough is enough; we just want a graceful exit for ourselves, no matter what happens to Iraq. To them it is a war we should never have started and the sooner we leave, the better.

But even if we can't agree on the failure or success of the Iraq War, we can come to some conclusions on the lessons we have learned.

We have known for a long time that President Bush and the Neocon’s vision of a peaceful, democratic, pro-American Iraq may never happen, or at least not for a very long time. At best it will be “Iraqracy,” as General David Petraeus calls it, two steps forward and one step back.

At worst it will be a broken state, and America will have spent nearly a trillion dollars and untold human sacrifice on a failed experiment.

We have learned the enormous difficulties of trying to force a country into a political system that the majority of its citizens neither want nor are prepared to sustain on their own.

But we have also learned, or re-learned, some lessons about committing U.S. combat forces overseas.

First, we must have a clear idea of their mission, what it is we expect them to accomplish. In Iraq, we fell into the trap of mission creep. Our initial casus belli was to find and eliminate Iraq’s weapons of mass destruction. When we didn’t find any, we stayed to topple Saddam Hussein’s government and dismantle his political party, military and government services. Once we had destroyed a brutal but none-the-less functioning government, we set up a U.S.-led Provisional Authority to replace it. And then we stuck around to help write them a constitution, hold democratic elections, form a government, and train new military and security forces.

The problem was, even though our mission grew, our resources didn’t keep pace, opening up a gap between what we wanted to accomplish and what we could realistically hope to accomplish. Without intending to, we set up a situation that was bound to fail. A civil war broke out, and we were caught in the middle.

Once President Bush committed to a surge in forces and narrowed the mission, we were able to get to the point we are today. Iraq is now a stable nation state, but it’s still a fragile situation. The surge has given us better odds at success, but doesn't guarantee it.

And, we've learned it’s a helluva way to fight a war. It’s not a plan we want to repeat as we figure out how to deal with the nuclear threat posed by an expansionist, potentially nuclear Iran, or the spread of terrorism through the Horn of Africa.

With the Iraq War we have relearned the lessons we learned and forgot after Vietnam:

- Have a clear mission going in.

- Make sure the resources are adequate to achieve that mission.

- Be honest with the American people about the costs in lives and treasure.

- Be prepared to adjust these as this war will go as all wars go – which is NOT according to plan.

Yet, the one lesson we should not take away from the Iraq War is that we can retreat into an era of isolation. Tempting as it may be, we cannot ignore new threats on the horizon in hopes they will go away. We no longer live in a world that will allow us to come home, pull up the drawbridge and retreat behind the moat. In today's world those threats will seek us out, not just knocking, but kicking down our door.

Kathleen Troia "K.T." McFarland is a Fox News National Security Analyst and host of FoxNews.com's DefCon 3. She is a Distinguished Adviser to the Foundation for the Defense of Democracies and served in national security posts in the Nixon, Ford and Reagan administrations. She wrote Secretary of Defense Weinberger’s November 1984 "Principles of War Speech" which laid out the Weinberger Doctrine. Be sure to watch "K.T." every Monday at 10 a.m. on FoxNews.com's "DefCon3" already one of the Web's most watched national security programs. 

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