By Ciara Finnegan, Maynooth University

International Humanitarian Law (IHL) is one of the oldest branches of International Law and in addition to being regulated by conventional and customary law, it is underpinned by the general principles of Distinction, Military Necessity, and Proportionality; all of which stem from the over-arching Principle of Humanity. These principles regulate IHL in the absence of conventional and customary rules, providing “guidelines in unforeseen cases”.[1] While Humanity constitutes “humanitarianism’s first principle” (Slim 1998, 28), it has remained “vague in several respects”[2] over the passage of time compared to its three derivatives which all “carry a particular, and well-defined, meaning in IHL”.[3]However, by remaining vague, the Principle of Humanity offers flexible protection in IHL and “holds primacy as a space of common ground” (Fast 2015, 113) in its role of filling the various lacunae in the IHL framework, offering a beacon of hope in the ‘fog of war’.

This central role of the Principle of Humanity as a beacon of hope is especially evident in modern IHL with respect to the area of Weapons Regulation. The flexible protection of the Principle of Humanity serves “to ‘humanise’ the conduct of war by imposing limits on the means and methods of warfare”.[4] Due to constant technological advancement, the imposition of limits on new weapons technologies which may be used in armed conflicts is a central concern. For this reason, the Principle of Humanity remains paramount in providing protection in the face of unforeseen challenges posed to Weapons Regulation in IHL.

The continuation of this important role was facilitated by the introduction of the Martens Clause of the 1899 Hague Convention II, which concretised the Principle of Humanity in international treaty law as follows:

“Until a more complete code of the laws of war is issued, the High Contracting Parties think it right to declare that in cases not included in the Regulations adopted by them, populations and belligerents remain under the protection and empire of the principles of international law, as they result from usages established between civilized nations, from the laws of humanity, and the requirements of public conscience.”

While codifying the Principle of Humanity, the Martens Clause maintained the flexibility of protection which makes it a “provision for centuries to come” (Pustogarov 1999, 129) in Weapons Regulation.

Relevance of the Principle of Humanity to Weapons Regulation

As “all codifications omit some matters” (Meron 2000, 80), the introduction of the Martens Clause offered a means by which these omitted matters could be addressed in IHL by offering the protection of the Principle of Humanity.  Thus, the Martens Clause was included in many IHL instruments, including Weapons Regulation instruments such as:

  • 1907 Hague Convention;
  • 1980 Convention on Prohibitions or Restrictions on the Use of Certain Conventional Weapons;
  • 1997 Anti-Personnel Mine Ban Convention;
  • 2008 Convention on Cluster Munitions;
  • 2017 Treaty on the Prohibition of Nuclear Weapons.

This continued relevance of the Principle of Humanity in Weapons Regulation in IHL is evident in the instances of the current debates surrounding Lethal Autonomous Weapons (LAWs) and the Introduction of Weapons into Outer Space respectively.

Lethal Autonomous Weapons (LAWs):

LAWs are robotic weapons which “will operate autonomously to locate their own targets and destroy them without human intervention” (Sharkey 2010, 376) and their development has caused much debate in the area of Weapons Regulation. In 2013, Human Rights Watch released a report titled ‘Losing Humanity: The Case Against Killer Robots’ based on the argument that LAWs should not be used in armed conflict situations by virtue of the Principle of Humanity, as enshrined in the Martens Clause. Taking the human out of the loop of decision-making in armed conflicts is unlikely to align with the Principle of Humanity because, as noted by the UN Special Rapporteur on Extrajudicial, Summary and Arbitrary Executions “[t]aking humans out of the loop risks taking humanity out of the loop”. The removal of humanity from weapons usage risks the making of miscalculated robotic decisions with regards to target identification, which would breach the Principle of Humanity, in addition to other principles of IHL. Thus, the flexible protection of the Principle of Humanity currently presents a limitation on the introduction of LAWs into armed conflicts as the use of LAWs could constitute a violation of IHL. Furthermore, the Principle of Humanity, as codified in the Martens Clause, is the cornerstone of the arguments put forward in favour of expressly prohibiting LAWs in conventional IHL. For example, Human Rights Watch’s proposal for the introduction of a pre-emptive ban on LAWs in IHL is based on the premise that LAWs would contravene the Martens Clause.

The Introduction of Weapons into Outer Space:

With NATO declaring Outer Space an ‘operational domain’ in late 2019, the introduction of weapons into Outer Space is another prevailing concern with regards to Weapons Regulation. The reactions of the international community to this prospect “will determine the very future of warfare, humanity’s use of space, and the nature of global peace and stability” (Onley 2013, 743). Thus, the Principle of Humanity and the Martens Clause constitute central considerations in the use of weapons in Outer Space because “space warfare, often thought to be the most technologically innovative form of warfare” (Ramey 2000, 128), constitutes a lacuna in IHL which is currently only being filled by the flexible protection of the Principle of Humanity. The introduction of weapons into Outer Space could constitute a violation of the Principle of Humanity and thus, a breach of IHL. Therefore, as activity in this area continues to develop, the protection currently offered by the Principle of Humanity must be considered by Space actors in order to observe compliance with IHL.

In conclusion, the over-arching Principle of Humanity in IHL has not been lost in the ‘fog of war’, but instead “remains as present as ever” (Evans 2013, 733) as a beacon of hope in the instances that IHL legislation never foresaw, particularly in the area of Weapons Regulation. The flexible protection offered by the Principle of Humanity, and the Martens Clause, ensures that the interests of humanity remain protected, especially in the face of advancing weapons technologies.


[1] Jean Pictet, Development and Principles of International Humanitarian Law (Martinus Nijhoff Publishers 1985) 59-60.

[2] Kietil Muiezinovic Larsen, Camilla Guldahl Cooper and Gro Nystuen, Searching for a ‘Principle of Humanity’ in International Humanitarian Law(Cambridge University Press 2012) 1.

[3] ibid 1-2.

[4] Nicholas Tsagourias and Alasdair Morrison, International Humanitarian Law: Cases, Materials and Commentary (Cambridge University Press 2018) 39.

This post was originally due to be presented as a poster at the SLSA 2020 Annual Conference in Portsmouth. The poster was also submitted as part of our online Poster Exhibition, and can be viewed here.