Aggression is Always Grave: A Reflection on Gravity as the Central Feature of Aggression in International Law

[Luciano Pezzano is a researcher and professor of human Rights at the University of Business and Social Sciences (UCES, Argentina) and lecturer of public international law at the National University of Cordoba (UNC, Argentina)]

In his recent post on Opinio Juris, Davit Khachatryan offers a very interesting reflection on the gravity of uses of force and the hierarchical position of aggression in international law.

I agree with Prof. Khachatryan’s main thesis: a regime change against the will of the people through the use of force is a serious violation of Article 2(4) of the Charter. It is, therefore, an act of aggression, graver than other illegal uses of force.

However, since his post is based on certain terminological aspects of the issue, I cannot share some of his arguments. In my view, the idea expressed in the title of the post, “Not All Aggression is Equal”, introduces a distinction amongst acts of aggression that could conspire against the core aspect of the issue: that gravity is the central feature of aggression, and it is what distinguish it from other illegal uses of force. With his ideas, Prof. Khachatryan gives me the opportunity to reflect on this issue, a topic sometimes overlooked in legal literature.

The purpose of this contribution is, therefore, offering some thoughts on gravity as the central feature of aggression in international law and its differences from other illegal uses of force. The analysis will show that the main thesis of Prof. Khachatryan can be maintained without introducing new categories of acts of aggression. 

Prof. Khachatryan’s Arguments

Although I agree with the main thesis of the post, I have certain problems with some of the terminological arguments, mainly with the following paragraph:

Regime-change aggression satisfies the gravity threshold more readily and more completely than ordinary uses of force, for several interconnected reasons. First, Article 2(4) does not itself rank violations of the prohibition on force; any unlawful threat or use of force is a breach, and the Charter creates no formal hierarchy among them. Second, Resolution 3314 lists qualifying acts of aggression without differentiating their gravity by reference to the aggressor’s political objective. The argument here operates at a different level: not that the black-letter texts establish a hierarchy, but that the Rome Statute’s gravity and character criteria already require the kind of qualitative differentiation that regime-change aggression most clearly satisfies.

It is true that regime-change aggression satisfies the gravity threshold and it is graver than other uses of force, but  that does not mean that it is more serious than other acts of aggression. This is the main issue in this post: since aggression is inherently grave, all acts of aggression are legally equal. By referring only to “ordinary uses of force” and not to “acts of aggression” in the first phrase, Prof. Khachatryan seems to share the idea, but the issue is not clear in the post. 

The Charter does create a certain sort of hierarchy among breaches of the uses of force. Although all violations of Article 2(4) are illegal, only those uses of force that amount to an “armed attack” (or, in the French text, more interesting for this analysis, “agression armeé”) allows self-defense under Article 51. Furthermore, aggression – the only international crime called by its name in the Charter – seems to occupy a special place: Article 1(1) makes reference to “the suppression of acts of aggression or other breaches of the peace”, thus implying that aggression is a species (the graver) of breach of the peace.

Although Article 3 of the Definition of Aggression does not differentiate the gravity of the acts listed, it contemplates gravity in paragraph (g) and, according to the chapeau, the list is subject to the provisions of Article 2, which also includes gravity. Therefore, the Rome Statute’s criteria does not introduce gravity in the discussion, but confirms its character as a central feature of aggression. In the following section, I will develop these ideas.  

The Distinction Between Aggression and Other Illegal Uses of Force

In the first place, as Prof. Kachatryan acknowledges in the very first paragraph of his post, not all the illegal uses of force (i.e. uses of force in contravention of Article 2(4) of the Charter) are equal. This issue is clear in both the Definition of Aggression (approved by resolution 3314 (XXIX) in 1974) and in the case law of the International Court of Justice. As Prof. Kachatryan stresses, the resolution and its annex is the authoritative definition of aggression in contemporary international law.

Resolution 3314 (XXIX) itself calls upon all States “to refrain from all acts of aggression and other uses of force contrary to the Charter of the United Nations” (para. 3). One can deduce that acts of aggression are a species of the illegal uses of force. Therefore, there are uses of force that are illegal but they do not amount to acts of aggression.

This distinction is very important, since the general definition of Article 1 of the Definition of Aggression seems to qualify all uses of force in contravention of Article 2(4) as acts of aggression. However, Article 1 in fine clarifies that its terms must be taken “as set out in this Definition”, and Article 8 provides: “In their interpretation and application the above provisions are interrelated and each provision should be construed in the context of the other provisions.” That means that one cannot isolate Article 1 from other provisions, especially from Articles 2, 3 and the Preamble of the Definition.

Those provisions offer the key in order to distinguish aggression from other illegal uses of force, since, as Prof. Kachatryan remarks, “not all force is equal: magnitude and gravity are legally relevant.”

Indeed, according to the Preamble of the Definition, “aggression is the most serious and dangerous form of the illegal use of force” (fifth paragraph). That means two important things: first, that what distinguishes aggression from other forms of illegal uses of force is its inherent gravity; and second, that there are not uses of force more serious than aggression.

The inherent gravity of aggression is confirmed in Article 2 of the Definition, according to which “the Security Council may conclude that a determination that an act of aggression has been committed would not be justified in the light of other relevant circumstances, including the fact that the acts concerned or their consequences are not of sufficient gravity” (emphasis added). “Sufficient gravity” (regarding either the act or its consequences) appears again as a central feature of aggression in order to distinguish it from other uses of force.

Finally, Article 3(g) qualifies as an act of aggression “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” (emphasis added). One can derive two ideas from the provision: first, that the acts of the so-called “indirect aggression” qualify as acts aggression only when they cross certain gravity threshold; and second, that the other acts listed in Article 3 –particularly the invasion, occupation and annexation in paragraph (a)– are per se grave uses of force. 

In its famous judgment in Nicaragua, the ICJ held: 

it will be necessary to distinguish the most grave forms of the use of force (those constituting an armed attack) from other less grave forms […]. Alongside certain descriptions which may refer to aggression, [the Friendly Relations Declaration] includes others which refer only to less grave forms of the use of force (para. 191). 

Although the Court did not refer to the Definition of Aggression in its reasoning (it recognized the customary nature of Article 3(g) in para. 195), it drew a distinction between aggression and the “less grave forms of the use of force”. Gravity is, of course, the central feature for the distinction.

The discussions on the so-called “gravity threshold” in Article 8 bis (1) of the Rome Statute confirm these ideas. According to the norm, the state conduct element of the crime of aggression is “an act of aggression which, by its character, gravity and scale, constitutes a manifest violation of the Charter of the United Nations.” The object and purpose of the clause is to ensure the criminal responsibility for the clearest and most serious cases of the illegal use of force by one state against another (Barriga and Grover, p. 532). There is, though, certain debate in the legal doctrine regarding the possible existence of acts of aggression that do not cross that gravity threshold (see Kreß, pp. 510-520). However, as I have argued elsewhere (p. 98), in the interpretation of Article 8 bis it is important having in mind Understanding 6 to the Kampala Amendments: 

It is understood that aggression is the most serious and dangerous form of the illegal use of force; and that a determination whether an act of aggression has been committed requires consideration of all the circumstances of each particular case, including the gravity of the acts concerned and their consequences, in accordance with the Charter of the United Nations.

The Understanding is clearly compatible with the provisions of the Definition of Aggression and it shares the same language, giving a clear sense of unity of all norms involved. In that context, accepting that there are acts of aggression graver than others seems logically and legally impossible. If an act of aggression were less grave than other acts of aggression, that act could not be “the most serious form of illegal use of force”, and therefore, it cannot be considered as aggression at all. By the other hand, if an act of aggression were graver than other acts of aggression, that act would be more serious than the “most serious form of illegal use of force”, and that is absurd.

The best way to interpret the threshold clause in Article 8 bis (1) and Understanding 6 is, therefore, seeing them as a confirmation that gravity is the central feature of aggression, in line with resolution 3314 (XXIX) and the ICJ’s case law (see Pezzano, pp. 113-166).

The rules of international responsibility also confirms gravity as the central feature of aggression. The prohibition of aggression is a jus cogens norm (see ILC Draft Conclusions on Jus Cogens); therefore, aggression will be a breach of that norm. But, since gravity is inherent to aggression, an act of aggression is by itself, a serious breach of an obligation arising under a peremptory norm of international law, according to Article 40 ARSIWA. Indeed, in the commentary to Article 40, the ILC held: “some of the peremptory norms in question, most notably the prohibitions of aggression and genocide, by their very nature require an intentional violation on a large scale” (para. 8). In other words, aggression is always a serious breach.

Final Remarks

In conclusion, there are not acts of aggression graver than others. There are, though, illegal uses of force graver than others, and those graver acts are acts of aggression. Gravity is, therefore, what distinguishes aggression from other illegal uses of force. The Charter of the United Nations, the Definition of Aggression, the Rome Statute and the ICJ’s case law confirm this idea.

Returning to Prof. Khachatryan post, this analysis shows that his main thesis can be perfectly maintained without introducing differences amongst acts of aggression. Regime-change aggression is undoubtedly a grave act, but a large-scale invasion followed by the annexation of large parts of the territory of a State, or massive attacks against a State infrastructure are also grave acts and must be qualified as aggression. These acts are, however, graver than other illegal uses of force, and this finding is compatible with Prof. Khachatryan’s conclusions.

I am very grateful to Prof. Khachatryan for his inspiring post, for stressing the need to discuss gravity as the central feature of aggression, and for his treatment of the relationship between aggression and self-determination, a topic that deserves more attention in legal literature.

Since aggression is the most serious form of illegal use of force, the gravest breach of the peace, the quintessential example of serious breach of jus cogens, and, in the words of the Nuremberg Tribunal and the ILC, “the supreme international crime”, it is very important not introduce differences in degree of gravity amongst acts of aggression. All acts of aggression are grave and have serious consequences under international law.