A frequently cited definition of terrorism is ‘the deliberate creation and exploitation of fear through violence or the threat of violence in the pursuit of political change’. This definition corresponds well to a list of characteristics derived from fifty academic definitions, with the top five characteristics being: 1) Violence; 2) political; 3) fear; 4) threat; and 5) psychological effects and anticipated actions. A key characteristic that makes terrorism analytically distinct from other forms of political violence is how violence, often of a spectacular kind, is used manipulatively (i.e., psychological effects and anticipated actions) to create a particular effect (i.e., fear) in a target audience. This is why theatre is a popular analogy for terrorism.
The Terror Reign during the French Revolution introduced the term “terrorism” to public discourse. However, other scholars argue that this form of terrorism is analytically distinct from what we today label terrorism, as the state was the perpetrator. Instead, they argue that the anti-Czarists of Russia in the 1880s is the first example of modern terrorism, characterised as violence perpetrated by a non-state actor. In addition, this was the time when targeting went from assassinations of high-level enemies to groups of people associated with this enemy.
Modern use of terrorism as a concept originates from the 1920s, when the United Nations-precursor League of Nations sought to establish a common definition. The League presented its first attempt in 1937, describing terrorism as ‘all criminal acts directed against a State and intended or calculated to create a state of terror in the minds of particular persons or a group of persons or the general public’. The deliberation among members states prior to settling on this definition brought up a number of contested issues that policy makers and scholars still grapple with today. While some states worried that “terrorism” could be misused by states to condemn all types of violence, others saw it as a too difficult task to reach consensus and proposed instead to refer only to specific criminal acts and leave the whole definitional task aside. Later, the United Nations avoided further definitional debate until the Munich Bombing in 1972, but was unable to agree on a mutual definition.
While modern terrorism has a long legal history, scholarly interest in the phenomenon gained traction in 1971 when David Rapoport conceptualized terrorism as an analytically distinct phenomenon from other types of political violence. Prior to Rapaport’s contribution, terrorism was referred to only as a tactic used in guerrilla warfare. Since 1971, research on terrorism has grown exponentially – especially since the 9/11-attacks in 2001.
Despite a growing volume in academic publications on terrorism, a consensus on the definition of terrorism is yet to be reached. One point of disagreement concerns whether terrorism should be confined to non-state actors only, or if states can also be involved in terrorism. For instance, the European Union’s definition, adopted by a number of states, specifies the perpetrator as an individual or a group, thus excluding state-based terrorism. The US makes an exception to this rule, defining an act as terrorism if it is state sponsored. Another point of disagreement concerns whether attacks against military targets can be regarded as terrorism, or if non-combatant targeting is a crucial feature of terrorism.
Different understandings of, and approaches to, studying terrorism can also depend on one’s philosophy of science. Two main paradigms characterise the field today: The realist paradigm and the constructivist paradigm. Realists argue that a terrorist act can be identified through a set of objective characteristics, such as the five listed above. Constructivists, predominately scholars of critical terrorism studies, counter that terrorism exists in the eye of the beholder, and labelling something or someone as terrorism or terrorists can be utilised to advance a political agenda and discredit political enemies. For instance, one of the most crucial NATO allies in the Syrian civil war, especially in the fight against the so-called Islamic State, the People’s Protection Units (Y.P.G), is designated as a terrorist organization by Turkey. The group has deep ties to the Kurdistan Workers’ Party (PKK), an organisation that is designated as a terrorist organization by both Turkey and the US due to its militant activity inside Turkey. This, and similar examples, open up for criticism that there is an inherent ideological and political bias in defining terrorism with consequential policy implications.
Terrorism as a tactic of fear and intimidation has been practiced for millennia. Frequently mentioned examples of ancient terrorism are the Hindu Thugs, operating for at least six centuries (600-1300) in India; the militant Assassins seeking to purify Islam from 1090 to 1275; and the Zealots-Sicarii, a splinter group of the Jewish Zealots who, in 70 CE, militantly opposed the Roman occupation of Judea. However, its modern-day use is closely related to the emergence of nation-states during the 19th century. As such, modern terrorism has manifested through four global waves distinguished by their ideological motivation and historical drivers: (1) Anarchist terrorism from 1880 to the 1920s; (2) anti-colonial terrorism from the 1920s to the 1960s; (3) new left terrorism from the 1960s to the mid-1990s; and (4) religious terrorism, predominantly of the Islamist variant, from the Iranian revolution in 1979 to present day. Out of these four waves, only the anti-colonial one has truly ended following the end of the colonial era. In addition, other predominant kinds of terrorism include ethno-separatist or nationalist terrorism, right-wing terrorism, animal rights terrorism, and environmentalist terrorism. Currently, mass-casualty attacks committed by lone actors groomed in extreme-right online subcultures has emerged as a new type of threat at the global level.
A number of databases covering terrorist incidents exist, enabling for temporal and spatial comparison. The most well-known database is the Global Terrorism Database (GDT). The GTD shows a sharp rise of terrorist attacks at the global level between 2004 and 2014, followed by a sharp decline. Other databases cover more specific regions or phenomenon, such as Terrorism in Western Europe – Events Data (TWEED), the United States Extremist Crime Database (ECDB), or the Right-Wing Terrorism and Violence (RTV) in Western Europe dataset. For instance, looking at ECDB and RTV, it becomes apparent that fatal right-wing attacks have decreased in the United States and Western Europe since the 1990s. For Western Europe, this is also the case if we only count attacks that are more terrorist-like in kind, such as premediated attacks using explosives or firearms.
Terrorism as a strategy usually implies manipulating public fear to trigger overreactions from the enemy by way of repression and unjust behavior towards the terrorists’ potential base of support, thereby creating increased sympathy and support for the terrorists’ cause. Considering the marginal risk of becoming a victim of terrorism in Western countries and the massive amount of resources used to counter this marginal threat, one could argue that the strategy seems to be working rather well. That said, due to the ineluctably political nature of terrorism, and its ambition of having far-reaching psychological repercussions beyond its immediate victims, much more is at stake than the risk of being attacked. Successful terrorist attacks can potentially alter the political dynamics of entire societies, and ultimately lead to fundamental societal changes. That is why political leaders still consider terrorism a major challenge to modern nation-states.
 Hoffman, B. (2006). Inside terrorism. New York, USA: Columbia University Press, 40.
 Schmid, A.P. (2011). The definition of terrorism. In A.P. Schmid (Ed.), The Routledge Handbook of Terrorism Research (pp. 39-98). London, UK: Routledge, 74.
 Cowen, T. (2006). Terrorism as theater: Analysis and policy implications. Public Choice, 128(1–2), 233–244.
 Brown, W.C. (2019). The pre-history of terrorism. In E. Chenoweth, R. English, A. Gofas, & S.N. Kalyvas, (Eds.), The Oxford handbook of terrorism (pp. 87-100). Oxford, UK: Oxford University Press.
 Ibid., 87.
 Richards, A. (2015). Conceptualizing terrorism. Oxford, UK: Oxford University Press.
 Ibid., 38.
 Rapoport, D.C. (1971). Assassination & terrorism. Toronto, Canada: Canadian Broadcasting Corporation (CBC Audio).
 Paret, P., & Shy, J. W. (1962). Guerrillas in the 1960’s. Naval War College Review, 15(5), 8.
 Easson, J.J., & Schmid, A.P. (2011). Appendix 2.1 250-plus academic, governmental and intergovernmental definitions of terrorism. In A.P. Schmid (Ed.), The Routledge Handbook of Terrorism Research (pp. 99-157). London, UK: Routledge, 139.
 Schmid (2011), 48.
 Ganor, B. (2002). Defining terrorism: Is one man’s terrorist another man’s freedom fighter?. Police Practice and Research, 3(4), 287–304.
 Breen Smyth, M., Gunning, J., Jackson, R., Kassimeris, G., & Robinson, P. (2008). Critical terrorism studies–an introduction. Critical Studies on Terrorism, 1(1), 1-4.
 Barnard, A., & Hubbard, B. (2018, January 25). Allies or terrorists: Who are the Kurdish fighters in Syria? The New York Times. https://www.nytimes.com/2018/01/25/world/middleeast/turkey-kurds-syria.html.
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 Rapoport, D.C. (2012). Fear and trembling: Terrorism in three religious traditions. In J.G. Horgan & K. Braddock (Eds.), Terrorism studies: A reader (pp. 3-26). London, UK: Routledge.
 Rapoport, D.C. (2013). The four waves of modern terror: International dimensions and consequences. In J.M. Hanhimäki & B. Blumenau (Eds.), An international history of terrorism: Western and non-Western experiences (pp. 282-310). London, UK: Routledge.
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