International Humanitarian Law (IHL) applies only in situations of armed conflict. It offers two systems of protection: one for international armed conflict and another for non-international armed conflict. The rules applicable in a specific situation will therefore depend on the classification of the armed conflict.

A) International armed conflict (IAC)

IACs occur when one or more States resort to the use of armed force against another State. An armed conflict between a State and an international organization is also classified as an IAC. Wars of national liberation, in which peoples are fighting against colonial domination and alien occupation and against racist regimes in the exercise of their right of self-determination, are classified as IACs under certain conditions (See Article 1, paragraph 4, and Article 96, paragraph 3, of Additional Protocol I).

B) Non-international armed conflict (NIAC)

Many armed conflicts today are non-international in nature. An NIAC is an armed conflict in which hostilities are taking place between the armed forces of a State and organized non-State armed groups, or between such groups. For hostilities to be considered an NIAC, they must reach a certain level of intensity and the groups involved must be sufficiently organized. IHL treaty law establishes a distinction between NIACs within the meaning of common Article 3 and NIACs falling within the definition provided in Article 1 of Additional Protocol II.

Common Article 3 applies to “armed conflicts not of an international character occurring in the territory of one of the High Contracting Parties.” These include armed conflicts in which one or more organized non-State armed groups are involved. NIACs may occur between State armed forces and organized non-State armed groups or only between such groups.

Additional Protocol II applies to armed conflicts “which 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.” (See Article 1, paragraph 1, of Additional Protocol II.) The definition of an NIAC in Additional Protocol II is narrower than the notion of NIAC under common Article 3 in two aspects.

1) It introduces a requirement of territorial control, by providing that organized non-State armed groups must exercise such territorial control “as to enable them to carry out sustained and concerted military operations and to implement this Protocol.”

2) Additional Protocol II expressly applies only to armed conflicts between State armed forces and dissident armed forces or other organized armed groups. Unlike common Article 3, Additional Protocol II does not apply to armed conflicts between organized non-State armed groups.

In this context, it must be kept in mind that Additional Protocol II “develops and supplements” common Article 3 “without modifying its existing conditions of application.” (See Article 1, paragraph 1, of Additional Protocol II.) This means that this restrictive definition is relevant only for the application of Additional Protocol II; it does not extend to the law of NIAC in general.


Simultaneous existence of IAC and NIAC

In certain situations, several armed conflicts may be taking place at the same time and within the same territory. In such instances, the classification of the armed conflict and, consequently, the applicable law will depend on the relationships between the belligerents. Consider this hypothetical example. State A is involved in an NIAC with an organized non-State armed group. State B directly intervenes on the side of the organized non-State armed group. State A and State B would then be involved in an IAC, but the armed conflict between State A and the organized armed group would remain non-international in character. If State B were to intervene on the side of State A, both State A and the organized non-State armed group and State B and the organized non-State armed group would be involved in an NIAC.


Main rules applicable in international and non-international armed conflicts

The rules for NIACs remain less detailed than those for IACs. For instance, there is no combatant or prisoner-of-war status in the rules governing NIACs. That is because States have not been willing to grant members of organized non-State armed groups immunity from prosecution under domestic law for taking up arms. Given the principle of State sovereignty and States’ reluctance to subject internal matters to international codification, it has proven difficult to strengthen the system of protection in NIACs. It should be noted however that the important gap between treaty rules applying in IACs and those applying in NIACs is gradually being filled by customary law rules, which are often the same for all types of armed conflict.


What law applies to internal disturbances and tensions?

Internal disturbances and tensions (such as riots and isolated and sporadic acts of violence) are characterized by acts that disrupt public order without amounting to armed conflict; they cannot be regarded as armed conflicts because the level of violence is not sufficiently high or because the persons resorting to violence are not organized as an armed group.

IHL does not apply to situations of violence that do not amount to armed conflict. Cases of this type are governed by the provisions of human rights law and domestic legislation.