United Nations

Article 2.4 of the United Nations Charter, signed in 1945 in San Francisco, spells out that “all Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations,” in accordance with the principle of pacific settlement of disputes.

Nonetheless, resort to armed force is authorized in two circumstances:

1. In the case of self-defense, individual or collective, authorized by Article 51 of the UN Charter.
2. In the context of collective measures of security adopted by the UN Security Council (Art. 42 of the UN Charter).

▸ Peacekeeping ▸ Self-defense

Article 39 of the Charter provides that the Security Council is the sole body competent to determine the existence of any threat to the peace, breach of the peace, or act of aggression, without giving any definition of aggression.

Because no consensus was found during the first working sessions of the General Assembly, the issue of the definition of aggression was postponed and transmitted to the United Nations International Law Commission (ILC). However, the ILC did not reach agreement on a definition, the Special Rapporteur having concluded in its report to the General Assembly in 1951 that aggression “by its very essence, is not susceptible of definition” (A/CN.4/44, p. 68). Several other special committees were entrusted by the General Assembly to propose a definition of aggression, but all failed in agreeing upon a consensual definition.

It was not until 1974 that the UN unanimously adopted a definition of aggression. Resolution 3314 of the General Assembly, which is based on the definition of aggressor proposed in 1935 during the Conference for the Reduction and Limitation of Armaments, defines aggression as “the use of armed force by a State against the sovereignty, territorial integrity or political independence of another State, or any other manner inconsistent with the Charter of the United Nations.” The General Assembly specifies that in this definition, the term “State” is used without prejudice to questions of recognition or to whether a State is a member of the United Nations, and includes the concept of a “group of States” where appropriate. According to the United Nations, the “first use of armed force by a State in contravention of the Charter shall constitute prima facie evidence of an act of aggression,” but this act must be of a “sufficient gravity” to be determined as such by the Security Council.

According to the UN General Assembly Resolution, the following acts constitute acts of aggression, regardless of a declaration of war, though they are not exhaustive:

1. The invasion or attack by the armed forces of a State of the territory of another State, or any military occupation, however temporary, resulting from such invasion or attack, or any annexation by the use of force of the territory of another State or part thereof;
2. Bombardment by the armed forces of a State against the territory of another State or the use of any weapons by a State against the territory of another State;
3. The blockade of the ports or coasts of a State by the armed forces of another State;
4. An attack by the armed forces of a State on the land, sea, or air forces, or marine and air fleets, of another State;
5. The use of armed forces of one State that are within the territory of another State with the agreement of the receiving State, in contravention of the conditions provided for in the agreement or any extension of their presence in such territory beyond termination of this agreement;
6. The action of a State in allowing its territory, which is placed at the disposal of another State, to be used by that other State for perpetrating an act of aggression against a third State;
7. The sending by or on behalf of a State of armed bands, groups, irregulars, or mercenaries to carry out acts of armed force against another State of such gravity as to amount to the list of acts listed above, or its substantial involvement therein.

This definition is based on three criteria: (1) the act of aggression must be perpetrated by a State and can engage the responsibility of such State; (2) it implies the use of armed force; and (3) it must reach a level of sufficient gravity in order to be qualified as such by the Security Council and give rise to reactions in self-defense or sanctions imposed by the international community. The definition excludes ideological and economical aggressions and does not provide for the possibility that these acts be perpetrated by non-state actors (armed groups or other entities).

It is to be noted that despite the adoption of this definition in 1974, the Security Council continued to use the more neutral terminology of the threat to peace and international security in its later management of international crisis, such as the successive invasions of Lebanon by Israel in March 1978 and June 1982, or the invasion of Kuwait by Iraq in August 1990, even though invasion constitutes an act of aggression in the General Assembly Resolution.

International Court of Justice

In its judgment, pronounced in the case concerning military and paramilitary activities in and against Nicaragua ( Nicaragua v. United States of America , June 27, 1986), the International Court of Justice interpreted the definition of aggression, holding that “while the concept of an armed attack includes the dispatch by one State of armed bands into the territory of another State, the supply of arms and other support to such bands cannot be equated with armed attack” (para. 247). The Court found that financial support, training, supply of weapons, intelligence, and logistic support constitute a clear breach of the principle of the non-use of force and the principle of non-intervention in the internal affairs of a State, that is, “a form of conduct which is certainly wrongful, but is of lesser gravity than an armed attack” (para. 247). It is to be noted that in the French version of this judgment, the phrase “armed attack” is translated as “agression armée.”

Moreover, the Court noted that indirect aggression within the meaning of Article 3.g of Resolution 3314 of the General Assembly shall, in order to be qualified as such, consist in “the sending by or on behalf of a State of armed bands, groups, irregulars or mercenaries, which carry out acts of armed force against another State of such gravity as to amount to (inter alia) an actual armed attack conducted by regular forces, or its substantial involvement therein” (para. 195). The Court considers that this description reflects customary law; “in customary law, the prohibition of armed attacks may apply to the sending by a State of armed bands to the territory of another State, if such an operation, because of its scale and effects, would have been classified as an armed attack rather than as a mere frontier incident had it been carried out by regular armed forces” (para. 195). By doing so, the Court limits the application of UN General Assembly Resolution 3314 since it implies that those “armed bands, irregulars or mercenaries” need to possess capacities of military strike equivalent to those of regular armed forces.

In its judgment of December 19, 2005, in a case concerning armed activities in the territory of the Congo ( Democratic Republic of the Congo v. Uganda ), the International Court of Justice found that the alleged aggression of the DRC against Uganda was not established in law because there was no satisfying evidence of a direct or indirect involvement of the DRC in armed attacks on the Ugandan territory perpetrated by armed groups operating from the Congolese territory (§146). According to the Court, these attacks did not emanate from armed bands or irregulars sent by the DRC or on behalf of the DRC, within the sense of Article 3.g of General Assembly resolution 3314 (XXIX) (para. 146). Consequently, the Court found that the legal and factual circumstances for the exercise of a right of self-defense by Uganda against the DRC were not present (para. 147). The incapacity of a State to control the activities of groups operating from its territory is not sufficient to establish the act of aggression, since an act of aggression has to be perpetrated by a State or forces acting under its control or on its behalf.

International Criminal Court

Originally, the Rome Statute of the International Criminal Court, adopted in 1998 and entered into force in 2002, did not provide a definition of the crime of aggression and conferred a theoretical competence to the Court in respect to this crime, notably because the UN Security Council was the only competent body to determine the existence of an act of aggression. The Rome Statute provided in its Article 5 that “the Court shall exercise jurisdiction over the crime of aggression once a provision is adopted in accordance with articles 121 and 123 defining the crime and setting out the conditions under which the Court shall exercise jurisdiction with respect to this crime. Such a provision shall be consistent with the relevant provisions of the Charter of the United Nations.” Articles 121 and 123 of the Statute establish the conditions for the amendment and revision of the Statute and notably provide that the UN Security General will convene a Review Conference of the Rome Statute seven years after the entry into force of the latter. The first Review Conference of the Rome Statute was held from 31 May to 10 June 2010, in Kampala, Uganda. During this conference, the Assembly of State Parties adopted a resolution that included a definition of the crime of aggression and a regime establishing how the Court will exercise its jurisdiction over this crime. The definition of the crime of aggression, proposed by the Special Working Group on the Crime of Aggression, is mainly inspired by the UN General Assembly resolution 3314 of 1974.

The definition is contained in the new Article 8 bis of the Statute and reads as follows:

1. “For the purpose of this Statute, ‘crime of aggression’ means the planning, preparation, initiation or execution, by a person in a position effectively to exercise control over or to direct the political or military action of a State, of an act of aggression which, by its character, gravity and scale, constitutes a manifest violation of the Charter of the United Nations.
2. For the purpose of paragraph 1, ‘act of aggression’ means the use of armed force by a State against the sovereignty, territorial integrity or political independence of another State, or in any other manner inconsistent with the Charter of the United Nations. Any of the following acts, regardless of a declaration of war, shall, in accordance with United Nations General Assembly resolution 3314 (XXIX) of 14 December 1974, qualify as an act of aggression:
3. The invasion or attack by the armed forces of a State of the territory of another State, or any military occupation, however temporary, resulting from such invasion or attack, or any annexation by the use of force of the territory of another State or part thereof;
4. Bombardment by the armed forces of a State against the territory of another State or the use of any weapons by a State against the territory of another State;
5. The blockade of the ports or coasts of a State by the armed forces of another State;
6. An attack by the armed forces of a State on the land, sea or air forces, or marine and air fleets of another State;
7. The use of armed forces of one State which are within the territory of another State with the agreement of the receiving State, in contravention of the conditions provided for in the agreement or any extension of their presence in such territory beyond the termination of the agreement;
8. The action of a State in allowing its territory, which it has placed at the disposal of another State, to be used by that other State for perpetrating an act of aggression against a third State;
9. The sending by or on behalf of a State of armed bands, groups, irregulars, or mercenaries, which carry out acts of armed force against another State of such gravity as to amount to the acts listed above, or its substantial involvement therein.”

By the insertion of this new article, the act of aggression becomes a crime engaging the individual criminal responsibility of those who perpetrated it, and not only the responsibility of the State.

The Elements of Crimes of the Court were also amended to specify the constitutive elements of this new crime. One of the elements asserts that the perpetrator must be one or more persons in a position effectively to exercise control over or to direct the political or military action of the State that committed the act of aggression. This definition is restrictive since it excludes the prosecution of members of non-state armed groups acting on behalf of a foreign State. Judicial prosecutions against commanders of such groups remain possible before the ICC under other crimes. Besides, recent jurisprudence suggests that attacks by non-state armed groups could be recognized by the judges as constitutive of an act of aggression if it is proven that these groups act as de facto agents of a foreign State.

Unlike other crimes in the Rome Statute, the crime of aggression is subject to more stringent conditions of referral. Indeed, with regard to the crime of aggression, the prosecutor may only proceed with an own motion ( proprio motu ) investigation or an investigation based on a State referral after first ascertaining whether the Security Council has made a determination of the existence of an act of aggression (under Article 39 of the UN Charter), where the situation concerns an act of aggression committed between States Parties, or when the Pre-Trial Division of the Court has authorized the commencement of an investigation if, six months after the event, the Security Council has not officially determined the existence of the act of aggression. Finally, the provisions of both Article 15 bis and Article 15 ter provide that the Court will not be able to exercise its jurisdiction over the crime of aggression until (1) at least thirty States Parties have ratified or accepted the amendments and (2) a decision is taken by two-thirds of States Parties to activate the jurisdiction at any time after 1 January 2017.

▸ International Criminal Court

Organization of American States

The Inter-American Treaty of Reciprocal Assistance, adopted in Rio de Janeiro, Brazil, in 1947, and the Charter of the Organization of American States (OAS), signed in 1948 in Bogota, Colombia, prohibits war of aggression, affirming that victory does not give rights to the attacking State (Art. 3.g of the Charter). According to the OAS, an act of aggression against one American State is an act of aggression against all the other American States (Art. 3.3 of the Treaty and Art. 3.h of the Charter).

Article 9 of the Treaty defines two types of aggression: (1) unprovoked armed attack by a State against the territory, people, or land, sea, or air forces of another State, and (2) invasion by the armed forces of a State of the territory of an American State. Further, Article 21 of the Charter stipulates that “the territory of a State is inviolable; it may not be the object, even temporarily, of military occupation or of other measures of force taken by another State, directly or indirectly, on any grounds whatever.”

Moreover, the OAS provides the possibility of other forms of aggression than armed attack (Art. 6 of the Treaty and Art. 29 of the Charter). The text does not give precision about this kind of attack, but one can think of economic aggression or diverted forms of political subversion and interference, which could fall into the category of “other measures of force” mentioned above.

African Union

On 31 January 2005, Member States of the African Union adopted the Non-Aggression and Common Defense Pact in Abuja, Nigeria. This Pact entered into force in 18 December 2000; it was signed by forty-three States but ratified only by twenty in June 2015.

Article 1.c of this Pact defines aggression more broadly than other international instruments as it goes beyond the acts committed against the sole territory and includes attacks perpetrated against the other two components of the State: political sovereignty and the population.

It proposes a broader definition than the ones proposed by the UN, the ICJ, and the ICC, providing the possibility that aggression be perpetrated by armed groups but also terrorist groups on the territory of a State (“any foreign or external entity”), and also by considering that any support by a State to armed groups, mercenaries, and other organized transnational criminal groups that may carry out hostile acts against a Member State can constitute aggression, which goes much further than the interpretation of the International Court of Justice (see supra).

“Aggression means the use, intentionally and knowingly, of armed force or any other hostile act by a State, a group of States, an organization of States or non-state actor(s) or by any foreign or external entity, against the sovereignty, political independence, territorial integrity and human security of the population of a State Party to this Pact, which are incompatible with the Charter of the United Nations or the Constitutive Act of the African Union. The following shall constitute acts of aggression, regardless of a declaration of war by a State, group of States, organization of States, or non-state actor(s) or by any foreign entity:

1. the use of armed forces against the sovereignty, territorial integrity and political independence of a Member State, or any other act inconsistent with the provisions of the Constitutive Act of the African Union and the Charter of the United Nations;
2. the invasion or attack by armed forces against the territory of a Member State, or military occupation, however temporary, resulting from such an invasion or attack, or any annexation by the use of force of the territory of a Member State or part thereof;
3. the bombardment of the territory of a Member State or the use of any weapon against the territory of a Member State;
4. the blockade of the ports, coasts or airspace of a Member State;
5. the attack on the land, sea or air forces, or marine and fleets of a Member State;
6. the use of the armed forces of a Member State which are within the territory of another Member State with the agreement of the latter, in contravention of the conditions provided for in this Pact;
7. the action of a Member State in allowing its territory to be used by another Member State for perpetrating an act of aggression against a third State;
8. the sending by, or on behalf of, a Member State or the provision of any support to armed groups, mercenaries and other organized trans-national criminal groups which may carry out hostile acts against a Member State, of such gravity as to amount to the acts listed above, or its substantial involvement therein;
9. the acts of espionage which could be used for military aggression against a Member State;
10. technological assistance of any kind, intelligence and training to another State for use in committing acts of aggression against another Member State; and
11. the encouragement, support, harbouring or provision of any assistance for the commission of terrorist acts and other violent trans-national organized crimes against a Member State.”

When acts of aggression have been determined under this Pact, the African Union can put in place mechanisms of collective security, though still embryonic, and Member States can submit recourses before the African Court of Justice.

▸ African Union ▸ Collective security ▸ International Criminal Court ▸ Public order ▸ Sanctions (diplomatic, economic, or military) ▸ Security Council of the UN ▸ Self-defense ▸ War