(Editor’s Note: This is Part I of a two-part series discussing issues of use of force, aggression, and armed attack in light of the 75th anniversary of the UN Charter. The series revisits the time between the conception and birth of the Charter in order to find new insights relevant to ongoing debates. This part provides a different understanding of the relationship between Article 2(4) and Article 51 of the Charter. Part II explains Article 51 as an exception to the authority of the Security Council to enforce peace and security)
On June 26, 1945, international law took a new path. After just a few months of drafting and negotiation, States signed the United Nations Charter. Several provisions govern the use of armed force. Two provisions dominate legal thought and practice. Article 2(4) prohibits the use of armed force. Article 51 permits self-defense if an armed attack occurs. Over the years, a standard view of their relationship has taken hold: a grave violation of Article 2(4) triggers Article 51, and Article 51 carves out an exception to Article 2(4).
The standard view is not incorrect, but it is incomplete. To arrive at a more complete view, we must travel a longer path. As we celebrate the Charter’s seventy-fifth birthday, we should revisit the months between its conception and its birth. There we will find new insight into ongoing debates.
Part One of this series shows that the right of self-defense under Article 51 is triggered by an act of armed aggression by one State against another. The understanding that a grave violation of Article 2(4) presumptively constitutes armed aggression crystallized decades later. So, today, a grave violation of Article 2(4) triggers article 51 because it constitutes an act of armed aggression.
Part Two of this series shows that Article 51 reflects an exception to the authority of the Security Council to take collective measures involving the use of force to suppress acts of aggression and maintain international peace and security. Article 2(4) contains an exception for such collective measures. Within the limits of Article 51, self-defense falls within the same exception because it supports such collective measures rather than undermining them.
As always, States may renounce this understanding and establish a new one. But to imagine a better future, we should first remember our past.
The Standard View
Article 2(4) of the Charter provides 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.
And Article 51 provides that
Nothing in the present Charter shall impair the inherent right of individual or collective self-defense if an armed attack occurs against a Member of the United Nations, until the Security Council has taken measures necessary to maintain international peace and security.
According to the International Court of Justice, “the most grave forms of the use of force” constitute an armed attack. It follows that grave violations of Article 2(4) trigger the right of self-defense under Article 51. The appeal of this view is obvious. The terms ‘force’ and ‘armed attack’ relate to the same general subject matter, yet presumptively carry distinct meanings. Force and armed attack share the same violent character, so they can differ only in their gravity and scale. The difference must be one of degree, since it does not appear to be one of kind. So an armed attack is an even more grave use of force.
Two important implications follow. First, an insufficiently grave use of force does not constitute an armed attack and does not trigger the right of self-defense. Among other things, the standard view entails that Iranian gunboats would have to use grave force against U.S. warships in order to trigger the United States’ right of national self-defense against Iran (see here and here).
Second, Article 51 does not permit the use of armed force targeting non-State actors on the territory of another State without its consent. Non-State actors cannot ‘use force’ within the meaning of Article 2(4), and so cannot carry out an ‘armed attack’ within the meaning of article 51. Put another way, non-State actors cannot violate Article 2(4), gravely or otherwise, and so cannot trigger Article 51. Among other things, the standard view entails that the invasion and occupation of large parts of Syria by the United States and Turkey violates the U.N. Charter (see here).
Needless to say, these implications are controversial, at least in the United States.
Aggression and Armed Attack
Yet States simply did not draw a direct connection between force and armed attack, or between force and self-defense, during the drafting or negotiation of the Charter. The closest connection we find lies in an alternative draft article proposed by Panama, according to which “a State may oppose by force an unauthorized use of force made against it by another State.” The Panamanian draft apparently received no discussion, so its import remains obscure.
In contrast, the drafters and negotiators consistently treated aggression as the trigger for legitimate self-defense. To the subcommittee responsible for Article 2(4), “it was clear . . . that the right of self-defense against aggression should not be impaired or diminished.” The drafters of Article 51 treated armed attack as a clear and grave form of aggression, as I explained in a previous post. The first draft circulated by the United States among the other Five Powers (China, France, the Soviet Union, and the United Kingdom) provided that
Should the Security Council not succeed in preventing aggression, and should aggression occur by any state against any member state, such member state possesses the inherent right to take necessary measures for self-defense. The right to take such measures for self-defense against armed attack shall also apply to understandings or arrangements like those embodied in the Act of Chapultepec, under which all members of a group of states agree to consider an attack against any one of them as an attack against all of them.
The Act of Chapultepec, to which the draft referred, was signed by American States just two months earlier. The Act considered “every attack of a State against … an American State . . . as an act of aggression” and contemplated the “use of armed force to prevent or repel aggression.”
Interestingly, the Pact of the League of Arab States, also signed in March 1945, also equated aggression and attack, providing that
In case of aggression or threat of aggression by a State against a member State, the attacked or threatened with attack may request an immediate meeting of the [League] Council.
This shows that many States understood aggression and attack as closely related concepts.
Back to Article 51. In response to the U.S. draft, one U.K. representative complained that “no one had been able to define aggression in thirty years.” Another “found the United States draft faulty in that it left open the problem of defining the aggressor state.” The U.S. representative (John Foster Dulles) stated that “the United States proposal attempted to define aggression in terms of ‘armed attack’ and in this way it was hoped to avoid the problem of trying to define aggression as such.” The term ‘aggression’ was dropped, and ‘armed attack’ became the trigger for both individual and collective self-defense.
Later negotiations also treated armed attack as a form of aggression. Alberto Lleras Camargo, the chairman of the relevant drafting committee, speaking as the delegate of Colombia, equated aggression and attack, saying that
if at any time an armed attack should ensue, that is, an aggression against a state which is a member of the regional group, self-defense, whether individual or collective, exercised as an inherent right, shall operate automatically within the provisions of the Charter, until such time as the Security Council may take the appropriate punitive measures against the aggressor state.
In the case of the American states, an aggression against one American state constitutes an aggression against all the American states, and all of them exercise their right of legitimate defense by giving support to the state attacked, in order to repel such aggression. This is what is meant by the right of collective defense.
Camargo, again speaking on behalf of Colombia, also said that
the right of defense is not limited to the country which is the direct victim of aggression but extends to those countries which have established solidarity, through regional arrangements, with the country directly attacked.
The delegates of Mexico, Costa Rica, Paraguay, Venezuela, Chile, Ecuador, Bolivia, Panama, Uruguay, Peru, Guatemala, El Salvador, Brazil, Honduras, and Cuba associated themselves with this latter statement. The French delegate added that, in his opinion, “the formula approved by the Committee extended in general to cases of mutual assistance against aggression.” The Soviet delegate noted that the draft article “deals with the right of a member of the Organization to self-defense in case of an act of aggression, until the Security Council takes measures for the maintenance of international peace.”
The understanding that an armed attack is an act of aggression left its mark on the final text. Chapter VII as a whole concerns “Action with respect to threats to the peace, breaches of the peace, and acts of aggression,” indicating that self-defense against armed attack is an action with respect to acts of aggression. The opening words “Should the Security Council not succeed in preventing aggression” were removed from the first draft, apparently “in order to eliminate the implication that the Security Council might ‘fail’ to maintain peace and security.” Yet the context of Article 51 preserves that implication. Under Chapter VII, the Security Council shall determine the existence of an act of aggression and decide what measures are necessary to maintain or restore international peace and security. States may defend themselves if an act of aggression constituting an armed attack occurs before, and until, the Security Council takes such necessary measures.
Notably, the French text of Article 51 uses the term “agression armée.” Article 1, article 39, and the heading of Chapter VII use the term “acte d’agression.” In this context, it seems natural to understand an agression armée as an acte d’agression involving armed force. Interestingly, the French text of Article 5 of the North Atlantic Treaty—which is supposed to track article 51 of the Charter—uses the term “attaque armée.” In my view, this makes the French text of article 51 an even more telling clue to its meaning. While the term “aggression” was removed from the English text, the concept of aggression remained: an armed attack is an armed aggression.
Aggression After 1945
As I noted at the outset, the standard view that a grave use of force constitutes an armed attack is not incorrect, only incomplete. Obviously, a grave use of force may constitute aggression, which in turn may constitute an armed attack. Indeed, in May 1945, Bolivia and the Philippines proposed that an attack by one State’s armed forces against another State’s territory, ships, or aircraft must be considered aggression. While States ultimately declined to define aggression in the Charter, such grave uses of force remained prototypical.
Subsequent practice in the application of the Charter has established the agreement of the parties regarding its interpretation, at least in some important respects. In 1974, the U.N. General Assembly declared that “[a]ggression is 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,” adding that “the Security Council may, in conformity with the Charter, 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.” The resolution went on to list prototypical cases of aggression, all of which involve the grave use of armed force.
More recently, the Statute of the International Criminal Court defines an “act of aggression” by reference to the General Assembly definition. On this basis, we can say that a sufficiently grave use of armed force presumptively constitutes armed aggression, and thereby presumptively constitutes an armed attack triggering the right of self-defense.
In light of this more complete understanding, we can see more nuance in the ICJ’s statement that “the most grave forms of the use of force” constitute an armed attack. This statement is often taken out of context from the ICJ’s judgment in Nicaragua v. United States—including by the ICJ itself. Most students remember that the ICJ relied on the General Assembly’s definition of aggression to conclude that “the sending by a State of armed bands to the territory of another State” can constitute an armed attack, depending on its scale and effects, while “assistance to rebels in the form of the provision of weapons or logistical or other support” cannot. They may forget that the ICJ also observed that
the question of aggression directed against Honduras and Costa Rica has fallen somewhat into the background. Nevertheless the allegation that such aggression affords a basis for the exercise by the United States of the right of collective self-defence remains on the record; and the Court has to note that Nicaragua has not taken the opportunity during the proceedings of expressly refuting the assertion that it has made cross-border military attacks on the territory of those two States.
This suggests that the ICJ itself viewed aggression as the trigger for self-defense, and armed attack as a form of aggression rather than force as such. This would explain why the ICJ looked to the General Assembly definition of ‘indirect’ aggression to determine when the actions of a non-State actor constitute an armed attack by a State.
During the Nicaragua proceedings, the United States asserted that
El Salvador, Honduras. and Costa Rica have each sought outside assistance, principally from the United States. in their self-defense against Nicaragua’s aggression. Pursuant to the inherent right of individual and collective self-defense. and in accordance with the terms of the Inter-American Treaty of Reciprocal Assistance, the United States has responded to these requests.
Tellingly, the terms of the Inter-American Treaty of Reciprocal Assistance (Rio Treaty) provide that “an armed attack by any State against an American State” trigger “the inherent right of individual or collective self-defense recognized by Article 51 of the Charter of the United Nations.” This suggests that the United States understood armed attack as a form of aggression.
Yet when the ICJ revisited self-defense in the 2003 Oil Platforms case, it did not discuss aggression at all. Instead, the ICJ simply relied on its previous statement:
As the Court observed in the case concerning Military and Paramilitary Activities in and against Nicaragua, it is necessary to distinguish “the most grave forms of the use of force (those constituting an armed attack) from other less grave forms,” since “In the case of individual self-defence, the exercise of this right is subject to the State concerned having been the victim of an armed attack”
On this basis, the ICJ concluded that
these incidents do not seem to the Court to constitute an armed attack on the United States, of the kind that the Court, in the case concerning Military and Paramilitary Activities in and against Nicaragua, qualified as a “most grave” form of the use of force.
The ICJ thereby severed the connections between force and aggression, and between aggression and self-defense—or at least concealed them. What began as one step in a longer argument—that grave force constitutes armed aggression, and armed aggression constitutes an armed attack—was presented as a basic axiom.
In 1945, an armed attack was an act of aggression. Today, an act of aggression is a grave use of force. So, today, an armed attack is a grave use of force. As promised, the standard view is not incorrect, only incomplete. Its important implications still follow. Insufficiently grave uses of force do not constitute aggression, so they do not constitute armed attacks, so they do not trigger the right of self-defense. Non-State actors cannot commit an ‘act of aggression’ within the meaning of the Charter, so they cannot carry out an ‘armed attack’ within the meaning of article 51, so article 51 does not permit the use of armed force targeting non-State actors on the territory of another State without its consent (see here).
By completing the standard view, we see the text of the Charter in a different light. We read Article 51 in the context of Chapter VII, and the Charter as a whole, and not merely in relation to Article 2(4). We confirm its meaning by recourse to the preparatory work. And we better understand how subsequent practice in the application of the Charter establishes the agreement of the parties regarding its interpretation. As always, States remain free to establish a different understanding and interpret the Charter anew. The future remains open. But the past is still with us.