This article looks at the emergence and evolution of the customary international humanitarian law applicable in situations of non-international armed conflict. In the years since the adoption of the Geneva Conventions and the Additional Protocols, a large number of rules relating to conduct in armed conflict have crystallised as customary international law, applicable in all instances of armed conflict. The significance of such development is that there are far fewer treaty rules regulating conduct in non-international armed conflict than in international armed conflict. Customary international humanitarian law has 'stepped in' to fill in many of the lacunae in the current treaty law of non-international armed conflict. It is now possible to speak of a comprehensive body of rules that are applicable in all instances of armed conflict. 21st century armed conflict continues to evolve and defy traditional definitions of armed conflict as mainly the preserve of sovereign States. Any harmonisation of the law relating to armed conflict can only be beneficial in ensuring that more of these non-traditional armed conflicts fall within the regulatory scope of the law of war.
When the 1974-1977 Diplomatic Conferences negotiated the draft of what would become Protocol II Additional to the Geneva Conventions of 1949, (1) the question arose as to where one of the enduring principles of the treaty law of International Humanitarian Law ('IHL'), the Martens Clause, (2) would go. (3) The Clause had been included in the body of Protocol I Additional to the Geneva Conventions, (4) as well as the four Geneva Conventions of 1949. (5) When debate turned to the place of the Martens Clause in Protocol II, the Diplomatic Conferences inserted the Clause in the Preamble only and not in the main body of the Protocol. More significantly, however, the traditional formulation of the Martens Clause was amended. The Martens Clause, as included in Protocol II, states that '... in cases not covered by the law in force, the human person remains under the protection of the principles of humanity and the dictates of public conscience.' (6) Though the reformulation broadened the scope of the Martens Clause from the categories of 'civilians' and 'belligerents/combatants' to simply 'the human person', it was at the same time significantly limited by dropping the reference to 'the law of nations/international law' and 'established custom.' The Commentary to the Additional Protocols explains that the deliberate omission of any reference to 'established custom' is:
... justified by the fact that the attempt to establish rules for a
non-international armed conflict only goes back to 1949 and that the
application of common Art 3 in the practice of States has not
developed in such a way that one could speak of 'established custom'
regarding non-international armed conflicts. (7)
However, less than thirty years later, the United Nations ('UN') Commission of Enquiry on Darfur noted:
... that a body of customary rules regulating internal armed
conflicts has thus evolved in the international community... some
States in their military manuals for their armed forces clearly have
stated that the bulk of international humanitarian law also applied
to internal conflicts. Other States have taken a similar attitude
with regard to many rules of international humanitarian law. (8)
In this respect, the Commission was referring to the military manuals of Germany and Britain, (9) and to a number of comments made by the United States over the previous decades, regarding what it considers to be the general principles governing conduct in internal armed conflicts. (10) The Commission on Darfur also noted that the inclusion of internal violations of IHL in the International Criminal Court ('ICC') Statute 'proves that the general legal view evolved in the overwhelming majority of the international community . …