Last Friday the United Nations Security Council agreed to impose a no-fly zone in Libya, after weeks of negotiations. There are fears that it may be too late to protect civilians or stop the forces of Libyan leader Moammar Gadhafi from crushing the armed revolt against him. Nevertheless, it does provide the authorization that external forces need to try to level the playing field against a leader who has shown no hesitation to slaughter his own people. Equally significant, it puts other tyrants on notice that they too do not enjoy immunity when they turn the power of the state against their own citizens.

There were scattered incidents in January, but protests in Libya gathered momentum in mid-February as demonstrators there took inspiration from upheavals elsewhere in the Arab world. Within days, several cities had thrown off the Tripoli government, and ranking officials, along with senior ambassadors, broke with Col. Gadhafi. A National Transition Council that sought to organize the disparate protest movements formed at the end of the month.

At first, it looked like Mr. Gadhafi would suffer the same fate as Mr. Hosni Mubarak, but there was a critical difference between the two: Whether the product of delusion or desperation, the Libyan leader refused to quit. He rallied against the rebels, and unlike other Arab leaders, was ready to use all the strength of the state against them. He has even reportedly hired mercenaries, fearing that his own troops might be reluctant to brutalize their fellow citizens.