According to UN Security Council Resolution 1973, the operation will "protect civilians and civilian-populated areas under threat of attack in the Libyan Arab Jamahiriya, including Benghazi, while excluding a foreign occupation force of any form on any part of Libyan territory."

The Secretary General of the Arab League, Amr Moussa, saw allied intervention as defensive: "The goal is to protect civilians first of all, and not to invade or occupy."

Similarly, the Chairman of the Joint Chiefs of Staff Mike Mullen claimed that the campaign could be a success even if Qaddafi remains in office: "the goals of this campaign right now are limited, and it isn't about seeing him go."

On the other side of the coalition are those who view the military as a sword to overthrow the tyrant. The UN resolution may prohibit an occupying army, but it also gives wide latitude to strike Qaddafi. Force can be used to protect "civilians" and also "civilian-populated areas under threat of attack"--virtually a blank check to attack the regime's military.

The French are firmly in the hawkish camp. Paris has already given diplomatic recognition to the Libyan rebels. One French government spokesman said that air strikes would "allow [the Libyan people] to go all the way in their drive, which means bringing down the Qaddafi regime." Meanwhile, British Prime Minister David Cameron claimed that Qaddafi "needs to go."

Secretary of State Hillary Clinton also used tough language: "if you don't get him [Qaddafi] out and if you don't support the opposition and he stays in power, there's no telling what he will do."

Meanwhile, Obama seems to be hedging his bets. The president avoided setting the target sights on Qaddafi, and described a "focused" mission to aid civilians. But Obama also said the Libyan dictator had lost "the legitimacy to lead" and must comply with far-reaching demands, including a ceasefire and a withdrawal of forces from Ajdabiya, Misrata, and Zawiya.

These divisions over war aims are not easy to paper over. After all, different objectives call for different tactics. If we're trying to alleviate suffering, we need to negotiate with Tripoli. But if we demand unconditional surrender, there's little point in talking.

The scope and difficulty of the missions also vary dramatically. We can readily stop the regime from conquering Benghazi--although this will hardly resolve the Libyan civil war.

But it's not at all clear how we achieve regime change. The UN resolution forbids an occupying army, and Obama has taken American ground forces off the table. The French called for the Libyan people to bring down the government. But we waited to act until Qaddafi had driven the rebels back to the gates of Benghazi. Now the rebels need to fight their way across North Africa again. Even with allied air cover, it could be a long road to victory.