The nature of terrorism will continuously change in the future as it has in the past. Yesterday, we worried about retail acts of terror—assassinations, bombings, and hijackings. Among the most difficult dilemmas was whether to give in to specific demands of the terrorists—usually the freeing of other terrorists. Today, we fear wholesale acts of terror—such as the use of passenger planes as airborne missiles directed against densely populated targets. Specific demands rarely accompany these acts. They are not contingent or conditional threats, or if they are, the conditions are deliberately set so high as to be unrealistic. Instead, ...