Terrorism, the unpredictable and apparently random use of violence against civilians and governments to create fear and to disrupt society, has been used for centuries as a means to achieve political goals. The September 11, 2001, attack on the World Trade Center and Pentagon was the one of the most destructive and dramatic acts of terrorism, but by no means the first against the United States. Recent terrorist acts and especially the threat of terrorism have, in ways reminiscent of the nuclear terror during the height of the Cold War, dramatically affected American society, culture, public policy, and even the nation's perceived identity.

While receiving less attention than the events of 9-11, there have been many instances of domestic terrorism in the United States, particularly during the period of social unrest over the Vietnam War in the 1960s. A number of indigenous terrorist groups developed from...