The evolution of terrorism as a legal concept in international law (1)



Abstract: This Article examines the evolution of the definition of terrorism at international law and tests the widely held view that international law does not provide a definition of terrorism. It contends that by abstracting from the common elements and themes present in the United Nations General Assembly and Security Council resolutions concerning terrorism, and the multi-lateral anti-terrorism conventions, treaties, and protocols, one can discern a core international law definition of terrorism. It concludes that until a customary international law rule prohibiting terrorism emerges or a comprehensive terrorism convention is concluded, states should draw on the international law definition of terrorism when drafting their domestic anti- terrorism legislation for legal and policy reasons, including to enhance the protection of human rights.

* Associate, Davis Polk & Wardwell, New York.


I. An Old Problem of Unsettled Scope


Opening his lectures at the Academy of International Law at The Hague in 1938, Antoine Sottile said of international terrorism: “The intensification of terrorist activity in the past few years has made terrorism one of today’s most pressing problems.”[1]

Such concerns have been frequently repeated over the last sixty-eight or so years. Terrorism’s grave threat did not start with Al Qaeda. Writing in 1977, M.K. Nawaz and Gurdip Singh quoted Sottile and added that the “verdict is no less true in our contemporary times.”[2] Popular opinion in the West would endorse the statement’s continuing cogency. Without being asked a question about terrorism, U.S. President George W. Bush referred to “terrorism” (or a variant of the word) twenty-two times in a 2004 televised inter view.[3] International terrorism is frequently cited by world leaders as the greatest threat to Western democracies, a claim made before[4] and after September 11, 2001.[5]

Notwithstanding the great concern about terrorism, it is most often said that no universally (or even widely) accepted definition of terrorism exists at international law.[6] Since at least the 1920s and 1930s many states have recognized terrorism as a transnational problem requiring a solution originating at international law. This Article examines the evolution of terrorism as a legal concept at international law and challenges the commonly accepted view that international law does not contain a definition of terrorism.[7] This Article contends that “terrorism” has a core, objectively determinable mean- ing at international law, and that one can discern such a definition from the existing sources of international law relating to terrorism.

The Article is divided into two main sections: Part Two examines the development of the definition of terrorism at international law and Part Three examines four definitions of terrorism in domestic law and considers whether (1) international law was influential in their formation and (2) the domestic definitions are consistent with the international definitional jurisprudence. Through treaty law, the international community has required signatory states to criminalize certain acts of terrorism by enacting domestic legislation. This approach to counter-terrorism makes the definitions of terrorism in domestic counter-terrorism legislation crucial to the effectiveness of international law’s response.

After contextualizing terrorism as a phenomenon, Part Two then examines the evolution of the definition of terrorism at international law. It first examines the failed efforts in the 1920s and 1930s to define terrorism and then considers the United Nations General Assembly’s resolutions with respect to terrorism and, more importantly, the resolutions of the United Nations Security Council. There are thirteen multi- lateral terrorism conventions, which have attracted widespread sup- port.[8] This Article analyzes their prohibitions and argues that a core definition of terrorism is discernable from the overlap of the conventions’ prohibitions and the themes present in each of the conventions.[9] This Article advances the proposition that states should draw on this core international definition of terrorism when enacting domestic definitions for both legal and pragmatic reasons, even though this minimum definition of terrorism has not attained customary international law status.

Part Three of the Article turns to the definitions of terrorism in domestic law. First, it considers the definitions in the United Kingdom, United States, India, and New Zealand (states that have experienced terrorism to varying degrees, but all of which enacted or significantly amended their counter-terrorism legislation after September 11), assessing whether international law influenced the formation of their definitions. Second, the substance of the four domestic definitions of terrorism is compared with the definition of terrorism at international law identified in Part Two.

The Article concludes that there is a core definition of terrorism at international law that provides guidance to states enacting terrorism legislation, but that to have an effect, states must look to international law and accept its guidance. Although the four domestic definitions are substantively similar to the international definition, all states should treat the international law definitional jurisprudence as setting a mini- mum level, not a maximum. The international definition of terrorism is destined to develop very slowly, and states need to tailor their legislation to specific national circumstances and respond to threats. The ease with which terrorists can cross borders means states cannot protect themselves simply by enacting and enforcing domestic legislation pro- scribing terrorism within their borders. Rather, every state must have legislation denying terrorists safe havens and safe places of operation. An established minimum international law definition of terrorism that informs states’ domestic criminal law is required to ensure a baseline of consistency and to facilitate international cooperation. The core definition identified in this Article provides that minimum as well as a yardstick against which to measure states’ legislation.

The existence of a definition of terrorism is important. It shapes states’ understanding of the problem, delimits their responses to it, and helps to distinguish lawful from unlawful responses. The perceived absence of an accepted international law definition is said by some largely to explain the inadequacy of international law’s ability to combat terrorism.[10] Do states share a common definition of international terrorism? Or at least, is there sufficient conceptual consensus to facilitate international cooperation in the “war on terrorism”? Is the enemy in the war sufficiently well defined to give “war” a real meaning?[11] Or is the enemy so broad to render speaking of “war” meaningless? Perhaps George Or well’s Nineteen Eighty-Four is pro- phetic?[12] Furthermore, many international instruments require states to take steps to fight terrorism. Without a clear definition of what to fight, states can unduly curtail civil rights and suppress political opposition under the pretext of fighting terrorism.[13] The grant of police powers triggered by terrorism without defining terrorism is inconsistent with the rule of law.


1 Antoine Sottile, Le Terrorisme International, in 65 Recueil des Cours 89, 91 (1938).

2 M.K. Nawaz & Gurdip Singh, Legal Control of International Terrorism, 17 Indian J. Int’l L. 66, 66 (1977); see also Bogdan Zlataric, Histor y of International Terrorism and its Legal Con- trol, in International Terrorism and Political Crimes 474, 474 (M. Cherif Bassiouni ed., 1975).

3 John V. Whitbeck, A World Ensnared by a Word; ‘Terrorism,’ Int’l Herald Trib., Feb.

18, 2004, at 6.

4 See, e.g., Guy B. Roberts, Self-Help in Combating State-Sponsored Terrorism: Self-Defense and

Peacetime Reprisals, 19 Case W. Res. J. Int’l L. 243, 247 (1987).

5 See, e.g., Xavier Baron, Newly-minted EU Anti-terror Unit to Study Casablanca Blasts, Agence France-Presse, May 19, 2003, available at (quoting Spanish Interior Minister Interior Angel Acebes); Jim Garamone, Iraq ‘a Grave and Gathering Danger,’ Bush Tells U.N., Am. Forces Press Service, Sept. 12, 2002, available at

6 See, e.g., Tel-Oren v. Libyan Arab Republic, 726 F.2d 774, 795 (D.C. Cir. 1984) (Ed- wards, J., concurring) (“[T]he nations of the world are so divisively split on the legitimacy [of terrorism] as to make it impossible to pinpoint an area of harmony or consensus.”), cert. den’d, 470 U.S. 1003 (1985); Flatow v. Islamic Republic of Iran, 999 F. Supp. 1, 17 (D.D.C. 1998) (citing U.S. Dep’t. of State, Patterns of Global Terrorism, at vi, 1, 17 (2003), available at (“Attempts to reach a fixed, universally accepted definition of international terrorism have been frustrated both by changes in terrorist methodology and the lack of any precise definition of the term ‘terrorism.’”); M. Cherif Bassiouni, International Terrorism: Multilateral Conventions (1937–2001), at 15 (2001) [hereinafter Bassiouni, Multilateral Conventions]; R.R. Baxter, A Skeptical Look at the Concept of Terrorism, 7 Akron L. Rev. 380, 380 (1974); Kevin J. Greene, Terrorism as Impermissible Political Violence: An International Law Framework, 16 Vt. L. Rev. 461, 462 (1992); Ileana M. Porras, On Terrorism: Reflections on Violence and the Outlaw, 1994 Utah L. Rev. 119, 125; Sami Zeidan, Desperately Seeking Definition: The International Community’s Quest for Identifying the Spectre of Terrorism, 36 Cornell Int’l L.J. 491, 491 (2004); Kenneth Watkin, Canada/United States Military Interoperability and Humanitarian Law Issues: Land Mines, Terrorism, Military Objectives and Targeted Killing, 15 Duke J. Comp. & Int’l L. 281, 294 (2005).

7 See sources cited in supra note 6.

8 See Appendix 1.

9 But see Jean-Marc Sorel, Some Questions About the Definition of Terrorism and the Fight Against its Financing, 14 Eur. J. Int’l L. 365, 365, 368 (2003).

10 Ved Nanda, The Role of International Law in Combatting Terrorism, 10 Mich. St. U. DCL J. Int’l L. 603, 604 (2001).

11 See Joan Fitzpatrick, Jurisdiction of Military Commissions and the Ambiguous War on Terrorism, 96 Am. J. Int’l L. 345, 347–50 (2002).

12 See generally George Or well, Nineteen Eighty-Four (1949) (describing a war of ambiguous scope and uncertain duration).

13 See, e.g., U.N. Human Rights Comm., Consideration of Reports Submitted by States Parties under Article 40 of the Covenant, Concluding Observations of the Human Rights Committee, Egypt,¶ 16, U.N. Doc. CCPR/CO/76/EGY (Nov. 28, 2002).