Although the term is not subject to a universally agreed definition, terrorism can be broadly understood as a method of coercion that utilizes or threatens to utilize violence in order to spread fear and thereby attain political or ideological goals. Contemporary terrorist violence is thus distinguished in law from "ordinary" violence by the classic terrorist "triangle": A attacks B, to convince or coerce C to change its position regarding some action or policy desired by A. The attack spreads fear as the violence is directed, unexpectedly, against innocent victims, which in turn puts pressure on third parties such as governments to change their policy or position. Contemporary terrorists utilize many forms of violence, and indiscriminately target civilians, military facilities and State officials among others.
The challenges of countering terrorism are not new, and indeed have a long history. The term "terrorism" was initially coined to describe the Reign of Terror, the period of the French Revolution from 5 September 1793 to 27 July 1794, during which the Revolutionary Government directed violence and harsh measures against citizens suspected of being enemies of the Revolution. In turn, popular resistance to Napoleon's invasion of the Spanish Peninsula led to a new form of fighter-the "guerrilla", which derives from the Spanish word guerra, meaning "little war" (Friedlander, 1976, p. 52). As a weapon of politics and warfare, however, the use of terrorism by groups can be traced back to ancient times, and as noted by Falk, "in various forms, terrorism is as old as government and armed struggle, and as pervasive" (Falk, 1990, pp. 39, 41). The focus of this module, and of the Teaching Module Series as a whole, is on terrorist violence and the threats carried out by non-State groups and the response of the international community, especially States, regional organizations and the United Nations system.