From my essay introducing The Atlantic's special coverage of the 10th anniversary of the 9/11 attacks:
What we saw on the morning of September 11, 2001 was evil made manifest. The terrorists who attacked the World Trade Center and the Pentagon (and tried to destroy the Capitol) claim to have been motivated by a theology of restoration -- a dream of restoring Islam to a position of global supremacy -- and by the politics of grievance. But something deeper undergirds these impulses: A compulsive need to murder one's way to glory. The stated goals of al Qaeda are flimsy excuses, meant to cover-up this ineluctable fact. The souls of men like Muhammad Atta and Khalid Sheikh Muhammad and Osama bin Laden are devoid of anything but hate, and murder is what erupted from these voids.
Let us stay on the subject of murder, because murder is the meaning of 9/11. Westerners are gifted in the art of slashing self-criticism, and so much of our discussion about 9/11 in the intervening years has centered on our failures -- real failures of intelligence and imagination that allowed the attacks to happen; presumed failures of foreign policy that gained al Qaeda sympathy among some Muslims; and failures in our response to radical jihadism, whether in Afghanistan, Iraq, or Guantanamo Bay, that are generally, though not universally, understood to have set us back in the war to defeat al Qaeda and its tyrannical and medieval ideology.