Exactly forty-six years ago, on December 14, 1974, the United Nations General Assembly adopted, by consensus, the Definition of Aggression, “the most serious and dangerous form of the illegal use of force.” The Definition was supposed to guide the Security Council in the exercise of its responsibility to “determine the existence of … any act of aggression and decide what measures shall be taken … to maintain or restore international peace and security.” In 2010, the Rome Statute of the International Criminal Court incorporated the Definition into the elements of the crime of aggression.

In the years leading up to its adoption, many States hoped the Definition would serve an additional purpose: to clarify the scope of the right of self-defense. Thirteen States proposed a draft declaration reflecting their view that anticipatory self-defense is unlawful, that self-defense against non-State actors in another State is unlawful, and that disproportionate force in self-defense is unlawful.

Other States agreed, in whole or in part. Just as importantly, several States disagreed, compelled by the draft declaration to openly express their contrary views. The result was perhaps the most substantive discussion of the right of self-defense by States since the drafting of the UN Charter itself. On the anniversary of the Definition’s adoption, this essay revisits the debates that led up to it and draws a possible lesson for our own time.

The Thirteen Powers

On July 3rd, 1968, Colombia, the Democratic Republic of Congo, Cyprus, Ecuador, Ghana, Guyana, Indonesia, Iran, Mexico, Spain, Uganda, Uruguay, and Yugoslavia submitted what became known as the thirteen-power draft (here, renumbered here). Its preamble equated armed attack with armed aggression, stating that “armed attack (armed aggression) is the most serious and dangerous form of aggression.” Its first article defined aggression as “the use of armed force, direct or indirect, by a State.” Its third article asserted that the right of self-defense “can be exercised only in case of the occurrence of armed attack (armed aggression) in accordance with Article 51 of the Charter.” These articles closely tracked a June 25 proposal by a group that included Algeria, Ghana, Guyana, Madagascar, the Sudan, Syria, and the United Arab Republic (Egypt).

According to these draft articles, the right of self-defense is triggered only if an armed attack by a State occurs. Anticipatory self-defense is ruled out, as well as self-defense against non-State actors operating without the direction or control of another State. In my view, these draft articles reflect the text, purpose, and drafting history of the UN Charter (see here, here, and here).

In the subsequent debates, a number of other States opposed anticipatory self-defense including Barbados, Chile, Congo, Cuba (also here), France, Iraq, Mali, Pakistan, and Romania, and the Soviet Union. These States endorsed the “priority principle,” according to which the first use of armed force between States constitutes aggression. Few States openly endorsed anticipatory self-defense (but see here and here), although other States may have opposed a strict priority principle in order to leave the question open. (The final text of the Definition provided that the first use of armed force constitutes prime facie evidence of aggression which “other relevant circumstances” may rebut.)

The thirteen-power draft also expressly recognized that the right of self-defense does not entitle a State “to take any measures not reasonably proportionate to the armed attack against it.” Many other States agreed that disproportionate force in response to an armed attack was unlawful, including Afghanistan, Costa Rica, Finland, Greece, Haiti, India, Kuwait, Libya, Madagascar, Malaysia, Mongolia, Pakistan, and Romania. Surprisingly, a number of States disagreed, including Guinea, Hungary, Israel, Mongolia, and Ukraine. Nevertheless, the International Court of Justice declared proportionality “a rule well established in customary international law” in 1986, and it is hard to imagine such opposition to it today.

Finally, and most controversially, the thirteen-power draft stated that

When a State is a victim in its own territory of subversive and/or terrorist acts by irregular, volunteer or armed bands organized by another State, it may take all reasonable and adequate steps to safeguard its existence and its institutions, without having recourse to the right of individual or collective self-defence against the other State under Article 51 of the Charter.

Supporters of this article essentially argued that “indirect aggression” seldom poses a grave threat to a State, but could provide a convenient pretext for unjustified force. Some conceded that “marginal cases” may arise “in which the infiltration was so substantial and the danger so great that they were tantamount to an armed attack and justified the exercise of the right of self-defence; it might perhaps be advisable to include a provision to that effect in the definition.”

Indeed, the final text of the Definition provided that “[t]he 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 [other acts that may qualify as aggression], or its substantial involvement therein,” may qualify as an act of aggression. Twelve years later, the International Court of Justice found that indirect aggression of such gravity “must be understood” as an armed attack triggering the right of self-defense.

Notably, no State explicitly challenged the thirteen-power draft’s assertion that only an armed attack by a State, directly or indirectly, triggers the right of self-defense. Armed groups operating without the direction or control of a State received little discussion. One State (Trinidad and Tobago) expressed the view that

armed attack initiated by one State against refugee or guerrilla camps of a national liberation movement located in the territory of another State [though] normally based on a self-defence argument …. must be condemned as illegal, since they involved the violation of another State’s territorial integrity.

Presumably, this view extended to other armed groups.

Notably, States were divided on the related question of “hot pursuit” of individual fugitives across international borders. Some States claimed that such “border incidents” were not acts of aggression or armed attacks, though they might constitute threats to the peace or breaches of the peace. Other States insisted that “deliberately pursuing a fugitive on the territory of a neighbouring State and opening fire on that territory without any intent to harm that other State … was strictly speaking an act of aggression.”

Fundamental Disagreements

These disputes over anticipatory self-defense, proportionality, and armed groups revealed deeper divides over the very nature of the modern right of self-defense. At one extreme, some States took the view that

the use of armed force by any State Member of the United Nations constituted an act of armed aggression because the international community forming the United Nations alone was authorized to use armed force. The right of self-defence was a right which the United Nations granted States as members of the international community and not an exception to the principle of the prohibition of the use of armed force.

Along somewhat similar lines, Mexico stated that

the right of self-defence, as defined in Article 51 of the Charter, had completely replaced everything which had existed on the subject in international law before the San Francisco Conference. There was now no legal standard, customary or conventional, bilateral or regional, which could be contrary to the mandatory and restrictive provisions of the Charter, since, according to Article 103 of the Charter, the provisions of the Charter were to prevail over those of any other international agreement. On the other hand, certain customary rules and established valid conditions with respect to subjects on which the Charter was silent, by laying down that there must be a direct link and a certain proportion between the unlawful act which gave rise to the act of self-defence and the defensive reaction.

At the other extreme, some States took the view that

the inherent right of individual or collective self-defence referred to in Article 51 of the Charter was a right which had existed throughout man’s history, enjoyed by all States under international law, independently of Article 51 by which it was in no way circumscribed. It was said that under this interpretation, self-defence was legitimate not only in the event of armed attack, but also in the event of a threat or a real danger of armed attack, in which case it was for the State concerned to decide whether the situation was such as to justify self-defence.

In between, various States took more moderate positions, for example that

the traditional concept of the right of self-defence had been modified under the Charter, and self-defence was truly justified only in the case of armed attack under the conditions indicated in Article 51. … It was also said that the provision in Article 51 enabled the victim to react immediately, before the Security Council took action; but the same provision required immediate reporting to the Security Council…. Furthermore, it was stated that self-defence must be subsequent to the attack. It was recalled in this connexion that at the Nurnberg trial the idea of preventive self-defence had been ruled out; the Charter too, left no room for doubt on the subject.

Along similar lines, Ecuador took the view that “only armed aggression, or armed attack, justified the exercise of the right of self-defence. That right had existed before the Charter; Article 51 did not create it. Moreover, it was exercisable solely as stipulated in Article 51, otherwise its exercise would constitute armed aggression.” In other words, the right of self-defense is inherent, but not unlimited (a view of the Charter that I share).


It is easy to forget this debate. These questions were never settled, or even put to a vote. For the sake of consensus, the final text made no direct reference to self-defense at all. In the words of the United Kingdom, the definition of aggression, “although vitally relevant to the question of self-defence, was not in itself a definition of the right of self-defence. Therefore, the well-known differences of opinion as to the nature and extent of the inherent right of self-defence preserved by Article 51 of the Charter had not been resolved by that definition.”

Today, Mexico once again seeks to clarify the scope of the right of self-defense or, at the very least, to invite open debate. To start the process, Mexico might compose draft texts reflecting the shared views of a group of likeminded States. These texts might then provide the focal point for a broader discussion within the international community. International law might progress. Failing that, the current impasse might be better understood. In taking this approach, Mexico would follow its own example, and that of the other twelve powers.


Image: Getty