The correct categorization of whether or not an armed conflict exists is important since this will determine whether or not IHL applies. This permits the lawful killing of some persons and destruction of certain property, whilst requiring the protection of others. IHL does not apply to all uses of inter-State confrontation nor to the employment of all forms of violence such as during riots or during isolated acts (see Additional Protocol II article 1(2)). It requires that a minimum threshold of violence is crossed first, or a military occupation occurs. Where this threshold is not met, then the rights and treatment of individuals will be determined by human rights law and any unlawful violence will be regulated by domestic criminal law. (Especially helpful in the drafting of this section was Melzer, 2016).
There is no treaty definition of 'armed conflict', including within the text of the Geneva Conventions 1949 or Additional Protocols 1977. Therefore, international case law, State practice and academic scholarship have been especially important in determining the legal meaning and parameters of this concept.
Two categories of armed conflict are identified under the existing treaty regime: international armed conflicts (IAC) occurring between two or more States; and (b) non-international armed conflicts (NIAC) which occur between State and non-governmental armed groups, or only between armed groups.
Significantly, the International Committee of the Red Cross (ICRC), as the guardian of IHL, has never recognized the existence of any global 'War on terrorism', nor does it consider non-State actors, perceived by some as having global reach - such as al Qaeda and ISIL and their affiliated groups - as being party to a global conflict. The ICRC does not consider that IHL applies beyond the geographical boundaries of the territory of parties to a conflict in a manner that permits the global targeting of any individuals believed (sometimes incorrectly) to be associated with non-State armed groups. Instead, the ICRC determines on a case by case evidential basis whether or not the criteria for the existence of an armed conflict have been satisfied.
The level of violence necessary to constitute an armed conflict differs between international armed conflicts (IAC) and non-international armed conflicts (NIAC). With respect to IACs, since there is a general prohibition against the use of force between States (as is reflected within article 2(4) United Nations Charter), it is generally presumed that any use of such military force which is governed by IHL is attributable to deliberate belligerent intent. This is regardless of the factors leading to the use of force or its degree of intensity. As the International Criminal Tribunal for the former Yugoslavia determined in the case of The Prosecutor v. Dusko Tadić a/k/a 'Dule' even minor instances of armed violence, such as an individual border incident or capture of a single prisoner, may suffice to cross the threshold for IHL to apply (1995, para. 70).
In an IAC context, under Common article 2 to the Geneva Conventions the two determining factors are: (1) the legal status of the belligerent parties to the conflict (normally States), and (2) the nature of the military confrontation between them (e.g. declared war, partial or total occupation of the territory of a State party to the Geneva Conventions). Under article 1(4) Additional Protocol I, for those States which are parties to it, the test in article 2 also extends to armed self-determination struggles. This means that the notion of being a party to a conflict in this situation can encompass certain categories of national liberation movements. Nowadays, IACs are the exception rather than the norm in terms of the prevalence of armed conflict situations.
In contrast to an IAC context, the threshold for non-international armed conflicts (NIACs) is significantly higher to allow for the fact that during peacetime law enforcement activities (including to counter terrorism) may necessitate the use of force against individuals or groups which is appropriately governed by domestic criminal as well as human rights law. Specifically, article 1(2) Additional Protocol II expressly excludes the following categories from coming within the scope of a NIAC: "situations of internal disturbances and tensions, such as riots, isolated and sporadic acts of violence and other acts of a similar nature, as not being armed conflicts", for these reasons.
Generally, the threshold is crossed when peacetime law enforcement approaches are unable to deal with the intensity of violence, thereby necessitating the deployment of the State's armed forces. The test for this, articulated by the International Criminal Tribunal for the former Yugoslavia, is the existence of a situation of "protracted armed violence" between a State and organized armed groups or between such groups ( Prosecutor v. "Dule", 1995, para. 70). Evidential factors for determining whether or not the armed conflict threshold test has been crossed in NIAC situations include:
[T]he number, duration and intensity of individual confrontations; the type of weapons and other military equipment used; the number and calibre of munitions fired; the number of persons and type of forces partaking in the fighting; the number of casualties; the extent of material destruction; and the number of civilians fleeing combat zones. The involvement of the UN Security Council may also be a reflection of the intensity of a conflict ( Prosecutor v. Haradinaj et al, 2008, para. 49).
Article 3 common to each of the Geneva Conventions governs persons taking no active part in hostilities in the case of an armed conflict not of an international character and seeks to guarantee minimum levels of protection for them. One significant effect that it has had is the recognition that parties to a conflict are not limited to States, but can also extend to non-State actors in this context. This is regardless of their legal personality, status or legitimacy under international law. They are, however, expected to be sufficiently organized such that they are able collectively to comply with IHL (something that is presumed for State parties to a conflict). This is through such factors as the existence of some form of command structure and accompanying disciplinary rules and mechanisms governing the group ( Prosecutor v. Haradinaj et al, 2008, para. 60).
Such requirements are reflected also in article 1(1) of the Additional Protocol II, which specifies that NIACs "take place in the territory of a High Contracting Party between its armed forces and dissident armed forces or other organized armed groups which, under responsible command, exercise such control over a part of its territory as to enable them to carry out sustained and concerted military operations and to implement this Protocol". The more extensive rights available under Additional Protocol II only apply in NIAC situations where the armed forces of the State on whose territory the conflict is taking place is a party to the conflict and the other criteria, such as effective control of at least part of the State's territory by the armed group is met. Otherwise, if the violence is only between non-State actors, Common article 3 alone will apply.
If the intervention by third-party States is to support an insurgency against the territorial State, the legal relationship between the territorial State and armed groups will remain the same (NIAC rules), whereas the armed confrontations between the States will be governed by IAC rules. If the degree of direction and control exercised by the third-party State over the insurgency group(s) is such that the group(s) could be considered to be military interventions by the State itself, the relationship between the groups and territorial State will be changed and also governed by IHL as a IAC. In situations where a third-party State or coalition of States intervene in a pre-existing NIAC situation to support the State on whose territory the conflict is occurring (an 'internationalized' armed conflict), thereby becoming a (co-belligerent) party to the conflict, IHL governing NIAC will continue to apply.
Sometimes the categorization of the conflict will change. For example, with respect to the US led coalition armed conflict with the governing Taliban regime in Afghanistan in 2001, initially this constituted an IAC. Once the Karzai Government was established and recognized internationally, the armed conflict became a NIAC with multinational forces present to assist the Afghan regime with its consent (Chatham House, 2012, p. 3).
Significantly, armed confrontation between other entities which do not fall into these strict categories cannot be treated under IHL as an armed conflict, but rather remain under the auspices of domestic law or NIAC depending on the level of violence. This is very important in the context of counter-terrorism since generally the non-State actor groups involved will fall into one of these two situations. In turn, the appropriate categorization determines which acts are provided for and which are not (IHL does not 'permit' types of fighting), and what rights may or should be available to them. The latter are less extensive under Common article 3 and Additional Protocol II compared with IACs, though should be regarded as the bare minimum with ideally more basic rights being given in practice.
Customary international law is of special importance for covering issues not specifically provided for under treaty law, hence the significance of the major ten-year study on customary international law undertaken by the ICRC (see 'tools' box 1). Even with its provision of rights and standards, determining the exact rights and boundaries of legality can often be less clear and more complex in a NIAC context compared with the more clearly defined and regulated IAC, e.g. regarding the treatment of detainees.
Historically, IACs tended to terminate hostilities with some intentional act such as a peace treaty, declaration of surrender or complete withdrawal from territory being contested. Nowadays, both IAC and NIAC tend to be marked by a more gradual, progressive reduction in the intensity of violence being used, ceasefires and/or the involvement of third parties such as peacekeepers, or the complete defeat of either party. Even once an armed conflict has ceased, elements of IHL will continue to apply, e.g., regarding the treatment of detainees/internees and various humanitarian endeavours until "... a general conclusion of peace is reached ..." ( Prosecutor v. "Dule", 1995,para. 70).