The president made it clear in his speech that the U.S.-led war against Libya is primarily motivated to prevent a humanitarian catastrophe. "We were faced with the prospect of violence on a horrific scale," he said. "To brush aside America's responsibility as a leader and - more profoundly - our responsibilities to our fellow human beings under such circumstances would have been a betrayal of who we are. Some nations may be able to turn a blind eye to atrocities in other countries. The United States of America is different."

This gives credence to the reports that Hilary Clinton, the secretary of state, Susan Rice, the U.S. permanent representative to the U.N., and Samantha Power, N.S.C. senior director for multilateral affairs, led the charge to war specifically to avoid "another Rwanda." The latter two especially have been outspoken in their belief that the United States was wrong not to intervene to stop the 1994 genocide in Rwanda in which the ethnic Hutu Interahamwe militia slaughtered some 800,000 fellow Rwandans in a few weeks while the world watched. One diplomat told Power she shouldn't let Libya become "Obama's Rwanda," according to the New York Times. Rwanda looms darkly in the liberal conscience as a powerful prod of guilt, whispering "Next time, do something. Do anything. Anything is better than nothing."

Liberals have a point about Rwanda. It was grotesque that troop-contributing countries actually withdrew their forces from the U.N. Mission in Rwanda (UNAMIR), rather than beef it up with more resources and authority, as the genocide unfolded. (However, Power betrays her ignorance of military realities when she argued in her book, A Problem From Hell, that the U.N. could have stopped the genocide with the assets it had on the ground at the time).

But Libya is not Rwanda. Rwanda was genocide. Libya is a civil war. The Rwandan genocide was a premeditated, orchestrated campaign. The Libyan civil war is a sudden, unplanned outburst of fighting. The Rwandan genocide was targeted against an entire, clearly defined ethnic group. The Libyan civil war is between a tyrant and his cronies on one side, and a collection of tribes, movements, and ideologists (including Islamists) on the other. The Rwandan genocidiers aimed to wipe out a people. The Libyan dictator aims to cling to power. The first is murder, the second is war. The failure to act in Rwanda does not saddle us with a responsibility to intervene in Libya. The two situations are different.

Advocates of the Libyan intervention have invoked the "responsibility to protect" to justify the campaign. But R2P is narrowly and specifically aimed at stopping genocide, war crimes, and crimes against humanity on a very large scale. It does not give the international community an excuse to pick sides in a civil war when convenient. Qaddafi has certainly committed crimes against humanity in this brief war, but R2P was designed to stop widespread, systematic, sustained, orchestrated crimes. If Qaddafi's barbarity meets that threshold, the administration hasn't made the case yet, and I'm not convinced. If R2P justifies Libya, then it certainly obligates us to overthrow the governments of Sudan and North Korea and to do whatever it takes to prevent the Taliban from seizing power in Kabul.

Historical analogies are sloppy thinking. U.S. policymakers went to war in Korea and Vietnam because they wanted to avoid another Munich. Liberals believe that Iraq is another Vietnam. Paleoconservatives worry that Libya is another Iraq, while liberals fear it is another Rwanda. These are rhetorical shortcuts that partisans use to excuse themselves from having to think very carefully or learn the details of each new case. One hopes the strategists in the White House will resist that temptation, but judging from Obama's speech, they aren't.