It will be 17 years next month since the West made the decision not to intervene in the Rwandan genocide, allowing more than 800,000 people to be slaughtered in just 100 days. Seventeen years later, President Obama has ordered military action in concert with the United Nations, to stop a new humanitarian crisis, this time in Libya, after the urging of a handful of aides. Among them were Samantha Power, who won a Pulitzer Prize for her book on the Rwandan genocide, and U.N. Ambassador Susan Rice, who was part of the team that failed to act in 1994.

According to reports, they advocated intervention to prevent massacres ordered by Moammar Gaddafi in the city of Benghazi and elsewhere. The threat of massacre, by all accounts, appeared to be imminent.

Rwanda’s upcoming anniversary, though, is not the central one that comes to mind. In a grim coincidence of history, President Obama ordered “Operation Odyssey Dawn,” establishing a no-fly zone in Libya, to begin on March 19, exactly eight years after President Bush began his shock and awe campaign in Iraq.

For many grappling with the potential consequences of the United States entering a third military conflict with a Muslim country, it may be difficult to decide which historical analogy is more apt — that of our long quagmire in Iraq or the humanitarian crisis we failed to avert in Rwanda.

But to my mind, there are two important lessons to be learned from the debacle in Iraq that very clearly override the Rwanda analogy.

The first of those lessons involves a matter of principle. I opposed the war in Iraq because it violated international law and, despite the fig leaf of an international coalition the Bush administration tried to wrap it in, the war was essentially an unjustified, unilateral campaign to militarily eliminate Saddam Hussein’s regime. We paid a heavy price for our blatant violation of international law and disregard for global opinion. Indeed, President Obama was elected in 2008, in part, to restore America’s moral standing in the world. Toward that end, I believe the president was right to resist the initial calls for unilateral U.S. involvement in Libya.

The president did what George W. Bush refused to do in 2003: He made U.N. Security Council approval and active regional support pre-conditions for U.S. military action. He also took steps to try limit America’s military footprint, letting France and Britain take the lead and ruling out sending ground troops into Libya.

The administration was also careful to negotiate a U.N. Security Council resolution that states its goal as the protection of civilians rather than regime change. As a matter of principle, the administration’s decision to seek U.N. Security Council action is an important step toward a multipolar world that operates according to multilaterally determined global law and in the interest of the global community.

But while the administration consulted the United Nations, it failed to seek congressional authorization. As with the Iraq war, the war in Libya is a war of choice. The president is undertaking this action without congressional authorization. This is a continuation of a dangerous — and unconstitutional — precedent, one that President Obama himself opposed as a senator.

“The president does not have power under the Constitution to unilaterally authorize a military attack in a situation that does not involve stopping an actual or imminent threat to the nation,” said Obama in December 2007. Since Libya does not present such a threat to the United States, one wonders how Obama squares his previous understanding of the Constitution with this military undertaking.

There is also a second set of lessons from the Iraq war relating to the costs and benefits of military action that should raise serious concerns about the White House’s decision.

As we learned or should have learned from the Iraq war, the use of military force can have all kinds of unintended consequences, especially in places we do not understand. The international coalition says it is going to war to prevent civilian casualties. But even with the most prudential use of military force, it’s not clear that we will be able to avoid civilian casualties by our own hands, as we see from our drone strikes within Pakistan.

And as civilian casualties mount, we may see this turn into a story of American overreach. Already we see the limits of the Arab League’s support, as it condemned the widespread bombing that came in the first day or two of the intervention. Until now, the democratic awakening has opened up the Arab world’s future because it has been undertaken by Arab peoples, who now believe they have control over their own destiny. The Libyan intervention risks changing that narrative.

Then there is the question of where this will all end. If anything, mission creep seems to be an inevitable feature of this kind of American military action. While the language of the U.N. resolution forbids “foreign occupation,” what will we do when chaos and small-scale humanitarian crises begin to occur across Libya?

Indeed, there is a troubling dimension to this intervention in that it reflects a mindset that associates U.S. foreign policy, whether alone or part of an allied, multilateral force, with heroic crusades to bring down the bad guys. It is that mindset that has done so much damage in the Middle East over the years and that has saddled us with the costly burdens of two ongoing wars.

The democratic awakening in the Arab world has presented the United States with an opportunity to put its past support for autocratic governments and repressive military and security apparatuses behind it. It offers this country a chance to align our interests with democratic change and economic progress. It would be a tragedy if the United States allowed the intervention in Libya to distract us from these difficult and important challenges. The most productive role for America in the Middle East — especially over the long-term — should primarily diplomatic and economic, rather than military.

Katrina vanden Heuvel is editor and publisher of The Nation. She writes a weekly online column for The Post.