In recent years, counter-terrorism measures have notably reshaped the relationship between terrorist suspects and the state. In this context, the discourse surrounding the lack of a uniform and comprehensive definition of terrorism at the international level has reoccurred. In the course of this contribution, clear lines will be drawn between the lack of an international definition of terrorism and certain transnationally important domestic trends relevant to the definition and countering of terrorism. Each section will focus on a particular aspect of the debate surrounding the term ‘terrorism’ with the aim of contextualising the development of the definitional vacuum and its impact on state counter-terrorism particularly after 9/11. It will be argued that an internationally binding definition of terrorism might not in fact have an impact on state counter-terrorism measures and domestic definitions of terrorism. This contribution will conclude that in the context of domestic and transnational legislative developments following 9/11, even if a definition of terrorism existed in international law, in practice there is no certainty that states will comply with it both in times of normalcy and emergency.

Who shall have the power to define international terrorism? To answer this question, which means determining the international public enemy, is an eminently political task. According to Carl Schmitt, politics is essentially about determining the public enemy. When it comes to a situation of emergency, whoever is in the position to distinguish friend from enemy holds ultimate power. While Schmitt was still thinking primarily in terms of the nation-state, the determination of the public enemy has now become an international issue. To demonstrate this point, this article examines the political struggle behind the legal debate on the definition of international terrorism. This is done by comparing two debates on international terrorism, one held in the 1970s and the other in the 2000s. Both these debates had, and still have, their institutional locus in the UN General Assembly and its Legal Committee. In the 1970s the non-aligned countries tried to challenge the discretion of the West in determining the international public enemy. In the 2000s the incumbent regimes of the Third World agree with Western states that terrorism is a common threat. The main cleavage is now between the leading Western powers that would like to determine the public enemy on a case-by-case basis (the United States and the United Kingdom), and the status quo states that would like to tie these hegemonic powers by a legal definition. It is precisely the absence of such a legal definition that makes it possible for the hegemonic powers and their followers to determine the international public enemy on a case-by-case basis. A legal definition would increase the coherence of the international coalition against terrorism and serve as a limitation on the discretionary power of the hegemonic states.

There have been numerous unsuccessful attempts to define terrorism generically in international treaty law since the 1920s, from early conferences on the unification of criminal law to efforts in the League of Nations, the International Law Commission, and the UN General Assembly. While these sources do not carry great weight as evidence of customary law, they illustrate the recurring normative and political disputes surrounding definition and elucidate the basic features of an international prohibition and/or crime of terrorism, as perceived by different international actors. The recurrent attempts at definition indicate that the international community attaches considerable normative importance to it. Drafting of a UN Comprehensive Terrorism Convention continues in the Sixth Committee, and the UN High-Level Panel on Threats, Challenges and Change advocated definition in treaty law in late 2004. Generic definition of terrorism can capture and stigmatize the political motives which distinguish terrorism from ordinary violent crime, or transnational organized crime for financial benefit. Following an historical pattern, agreement on the scope of any exceptions to a definition of terrorism remains the key obstacle, although much of the argument about exceptions is ideological, not substantive.