Imagine if we had assassinated Usama bin Laden in 1995. No September 11. No Afghanistan War. No Iraq War.  Without Usama bin Laden, the world  be an infinitely better and safer place today.

That's the equivalent of what happened in Pakistan this week. An American drone aircraft wasted Pakistan's Usama-in-Waiting, Baitullah Mehsud in South Waziristan.

Mehsud was one of the nastiest characters on the planet. He is thought to be behind Benazir Bhutto's assassination in 2007. He was the mastermind of  the wave of suicide bombings in Pakistani cities. He was the godfather of a new type of suicide bomber -- young children under the age of ten who he had strapped with explosives and sent out on suicide missions. He was the leader of the Pakistani Taliban, and closely associated with Al Qaeda and their host and collaborator.  He was bent on bringing down the Islamabad government.

To give you some idea of what Mr. Mehsud's fondest thoughts were, how's this sound:  "We want to eradicate Britain and America, and to shatter the arrogance and tyranny of the infidels. We pray that Allah will enable us to destroy the White House, New York and London." His weapon of choice? Pakistan's hundred or so nuclear weapons.

Mehsud's death is significant not only because it removes a potential mass murderer from the planet, but also because the way he was killed. The Taliban leader has been targeted for months, with American Predator drones flying high and out of site, waiting for the moment it had a clear shot. When Mehsud did venture out of doors, onto the rooftop of his father-in-law's house, he was immediately killed in what would have seemed to those standing near him, like a lightening bolt from the heavens. What Mehsud's death, and the recent death of Usama bin-Laden's son, tells every other terrorist leader is: you can run, but you can't hide. We have finally found a way to turn the tables on terrorists: they are the ones who now have something to fear, they are the ones who can attacked without notice.

The War on Terrorism is by no means over. We remain the number one target of a lethal band of Islamic jihadists bent on our destruction. But to paraphrase  Winston Churchill,  Mr. Mehsud's death may not mark the beginning of the end.  But it is, perhaps,  the end of the beginning for Al Qaeda.

Kathleen Troia "K.T. "McFarland served in national security posts in the Nixon, Ford and Reagan administrations.  She is a Distinguished Senior adviser to the Foundation for the Defense of Democracies.