The new, emerging standard presumes that even genocide may not spur nations to action if the risks of intervention are too high, as they are perceived to be in, for example, Darfur, where viable plans have called for thousands of ground troops. Yet crises short of genocide, such as the Libyan conflict, justify a military response when it can save thousands of lives with reasonable prospects of virtually no or only very low casualties to international allies.

Libya clearly met the threshold of state-sponsored mass murder. Starting February 17, about 75 percent of Libya broke away from Qaddafi's rule, prompting a government campaign of suppression using tanks, air power, and heavy shelling of urban areas. The estimated death toll by governments and knowledgeable observers ran into the thousands, with hundreds of thousands fleeing Qaddafi's wrath.

Bosnia and Kosovo saw similar levels of violence. By March 1993, when the United Nations authorized military action to protect Bosnian Muslims, thousands were almost surely dead and hundreds of thousands were refugees. By April 1999, when NATO authorized military action to protect Kosovar civilians, again thousands had been killed and hundreds of thousands were fleeing. International, morality-driven action almost certainly saved thousands of lives in each case.

Yet these experiences, and the negative example of the Iraq war, also teach a degree of realism. Intervention for humanitarian goals cannot justify large-scale risks to our own people. Serious consideration of international moral action requires practical, case-by-case assessments of the feasibility of military intervention with very low risks.

Libya presents as low a risk as any military mission the U.S. has pursued in the past 20 years. Qaddafi's threat to civilians rests on his ability to attack with concentrations of heavy weapons and to cut off supplies into ports -- both of which we can substantially blunt with very low risk to ourselves. The main reason for confidence is, simply, geography. To reach the population centers on along the Mediterranean coast, Qaddafi's heavy forces must expose themselves along easily identifiable routes in open desert terrain, within range of international air power stationed on naval ships at sea or on land bases in Europe and elsewhere.

Within the first week of international intervention, the threat to Benghazi and the east was vastly reduced at no loss of life to the U.S. or other members of the coalition. Given the large number of Libyans seeking to govern themselves, there is reason to think they can stand on their own and once again secure control over much of Libya. That is likely to require the re-establishment of pre-existing lines of economic shipments to the area -- the crucial next step, and another area where the U.S. and the world can help.