[T]he aim and the work of the terrorists [is] to keep the targeted population in the grip of fear. Here is how the Department of Defense describes the defining goal of terrorism:

"the calculated use of unlawful violence or threat of unlawful violence to inculcate fear; intended to coerce or to intimidate governments or societies in the pursuit of goals that are generally political, religious, or ideological."

Terrorists don't expect to achieve their goals through the physical destruction of a society using violence, the way a nation at war attempts with its military. The violence inflicted by terrorists is simply a tool for ratcheting up the fear level, and the fear of the violence, rather than the violence itself, is the primary tool of the terrorist. The greater the fear of the targeted population, the closer the terrorists are to achieving their goals.