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Defining Terrorism: The Necessity of a Universal Definition to Protect Fundamental Freedoms

By: Alexa August


The international community has attempted to formulate a comprehensive definition of “terrorism” since the days of the League of Nations, to no avail. Defining terrorism is inherently political, as one man’s freedom fighter is another man’s terrorist. International instruments predominantly do not contain a definition of terrorism due to its political sensitivities and a desire to obtain broad acceptance by States. This lack of a universal definition facilitates States’ politicization and misuse of the definition of terrorism to justify suppressing their citizens’ fundamental rights in the course of counterterrorism efforts. The emerging trend of a customary definition of terrorism in international law would be an essential tool for enabling domestic legal actors to challenge definitions of terrorism, which are being manipulated politically to criminalize expressions of fundamental human rights.

A Universal Definition of Terrorism is Crucial to Safeguarding Fundamental Freedoms

The International Framework for Defining and Criminalizing Terrorism

The international framework for criminalizing terrorism is comprised of United Nations Security Council Resolution 1373 (2001) and Security Council Resolution 1566 (2004), neither of which comprehensively define terrorism under international law. S.C. Res. 1373, passed in the days following 9/11, obliged States to take national legislative action to prevent and punish terrorism but did not define it, resulting in a mixed bag of domestic legislation that varied according to individual States’ distinct legal traditions. Consequently, States were concerned that S.C. Res. 1373 did not require adherence to international human rights standards in implementing their counter-terrorism obligations. To remedy these concerns, the U.N. Security Council passed S.C. Res. 1566, which does not define terrorism, but includes general descriptions of terrorist acts and does not criminalize any additional conduct that does not already constitute an offense under international conventions and protocols relating to terrorism.

This international framework does little to ameliorate human rights concerns without an established universal definition of terrorism. The Counter-Terrorism Committee, tasked with implementing S.C. Res. 1373, initially declared that human rights compliance was outside the scope of the Committee’s mandate. Amidst pressure, the Committee later adopted non-binding “policy guidance” by which States should merely “remain aware” of human rights.

A Customary Definition is Emerging in International Law But Does Not Yet Provide Protection for Human Rights

Despite the lack of a universally accepted definition of terrorism, recent trends signal an emerging customary definition of terrorism in international law. Binding customary international law is established through the widespread and consistent practice of States followed out of a sense of legal obligation (opinio juris). In 2011, the Special Tribunal for Lebanon found that a definition of “transnational terrorism” exists in customary international law, at least in time of peace. Critics refuted the Tribunal’s notion that a customary definition has crystalized, stating that, at best, the specific offenses of terrorism contained in treaties have become customary (e.g. aircraft hijacking, hostage taking, etc.) but that declaring the existence of a customary definition was premature.

An international consensus regarding elements of the definition of terrorism can also be inferred from the UN Draft Comprehensive Convention Against International Terrorism.  However, whether acts of armed forces during armed conflicts (i.e. the relationship between terrorism and international humanitarian law) or acts by government armed forces in times of peace (i.e. cases of “state terror”) constitute “terrorism” is still controversial. Further, it only covers transnational offenses, not domestic, which is the realm in which States most often utilize terrorism legislation to criminalize legitimate attempts to institute change in government policy.

Implications for the Lack of a Universal Definition of Terrorism

The lack of a model universal definition of terrorism risks domestic politicization and misuse of a State-created definition of terrorism to suppress citizens’ fundamental human rights through counterterrorism efforts. A recent example is Nicaragua’s amendment of counter-terrorism legislation to include “destruction of public or private property with the objective of intimidating the population or altering the constitutional order…” as an act of terrorism, which has been used to detain anti-Ortega protesters and try them in secret military courts without fundamental safeguards. This overly-broad definition of terrorism, including destruction of property to invoke constitutional change as a terrorist act, does not fit within the purported customary definition declared by the Tribunal, nor the definition set forth by the Draft Comprehensive Convention. However, due to the reluctance of the international community to accept a customary definition of terrorism, coupled with the non-binding and narrow nature of the Draft Comprehensive Convention’s application only to transnational terrorism, there is currently no recourse. A customary definition of terrorism would provide an essential tool for domestic legal actors to challenge definitions of terrorism, which are being manipulated politically to criminalize legitimate expressions of fundamental human rights, in domestic and international courts.


Summarizing the international community’s frustrations in defining terrorism, one academic appropriately stated, “Above the gates of hell is the warning that all that enter should abandon hope. Less dire but to the same effect is the warning given to those who try and define terrorism.” Despite this cynical warning, efforts to develop a universal definition of terrorism are crucial for protecting fundamental human rights and should not be abandoned.


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