Home EJIL Analysis The Contribution of the International Court of Justice and the Law of the Use of Force

The Contribution of the International Court of Justice and the Law of the Use of Force

Published on November 18, 2011        Author: 

At the end of October,  I had the pleasure of spending a few days at the UN in New York where I was invited to speak to the annual meeting of the Legal Advisers of Foreign Ministers of Member States of the UN. The annual meeting of Legal Advisers is held during what has come to be known as International Law Week at the UN. The meeting takes place during the period in which the International Law Commission’s report is being debated in the Sixth (Legal) Committee of the General Assembly and around the time the President of the International Court of Justice delivers its annual report to the UN. In the period I was there the President of the International Criminal Court also spoke to the General Assembly. It was also an interesting time to be there because this was the time in which candidates for elections to the various UN legal bodies show up in New York to “campaign” (if that is not too ugly a word). There are also a number of receptions held in the evenings by State’s missions to the UN to promote their candidates. There are quite a number of elections to legal bodies this year so there was a lot of this sort of promotional activity. This year there are elections to the ICJ (see here), elections to the International Law Commission (which were held yesterday), elections for ICC Prosecutor and for a number of ICC judges.

The annual meeting of the Legal Advisers was a 2 day affair and I was invited to speak on a panel on the Contribution of the International Court of Justice to the Development of International Law. My co-panellists were President Hisashi Owada of the ICJ and UN Under-Secretary General Patricia O’Brien (the UN’s Legal Counsel). The panel was chaired by Ambassador Anders Ronquist who is the Director General for Legal Affairs at the Swedish Ministry for Foreign Affairs (and sitting to my right was Alan Kessel the Legal Adviser of the Canadian Dept of Foreign Affairs who was one of the co-ordinators of the Meeting of Legal Advisers).

President Owada spoke about the contribution made by the ICJ through it’s advisory jurisdiction. Patricia O’Brien spoke about the contribution of the ICJ to the development of the law relating to the UN touching in particular on questions of personality and immunity. I spoke about the contribution of the ICJ to the development of the law relating to the use of force. My speech is below. There was an interesting question and answer session following our session and I got lots of good questions about issues I covered as well as questions about issues I did not cover (eg about cyberwarfare).


INTRODUCTION – The Court, the Maintenance of Peace and the Law on the Use of Force

It is easy to forget that since the role of the International Court of Justice is to allow for the peaceful resolution of international disputes: it is an instrument for maintaining international peace. Around the time when he was elected to the International Court of Justice, Sir Hersch Lauterpacht, one of the most famous international lawyers of the 20th century, wrote a book on The Development of International Law by the International Court.  In the very first sentence of that book, Sir Hersch Lauterpacht stated that:

“It would appear that the primary purpose of the International Court . . . lies in its function as one of the instruments for securing the peace in so far as this aim can be achieved through law”.

He then noted the obstacles that had prevented the Court at the time from being a significant instrument for maintaining international peace. However, he went on to suggest that though the Court had not been able to contribute directly to international peace it had done so indirectly by contributing to the development and clarification of the rules and principles of international law.   So the Court contributes to international peace in two ways (i) by settling disputes, the aggravation of which may lead to international tension and (ii) by developing rules of international law, which in turn provides a basis for peaceful relations among States. However, there is a third way in which the Court may contribute to the maintenance of peace. This third way is when the Court is called upon to deal with disputes concerning the use of force and thus disputes in which the peace is not only threatened but has been breached. In such cases the Court’s contribution to the peace is much more direct and this third way combines the previous two as well.

The very first contentious case before the International Court of Justice, the Corfu Channel Case (UK v Albania)  was a case involving the use of force. However, the issues placed before the Court in that case did not relate to the law on the use of force but rather the underlying dispute. It was not until the mid 1980s, in the Nicaragua Case (Nicaragua v USA),  that the Court had the first opportunity to pronounce on the law relating to the use of force. Since that case, the Court has been called upon much more frequently to decide disputes relating to the use of force, and it appears to be the case that much more now than when Hersch Lauterpacht wrote, States have confidence in the Court to deal directly with breaches of the peace. Since Nicaragua, the Court has been asked to decide cases involving the use of force in at least two advisory opinions and in nothing less than 26 contentious cases.  Not all of these cases have been decided on the merits and it was not in all cases that the Court pronounced on the law relating to the use of force.

The law on the use of force is the cornerstone of post World War II legal order and is to be found in two main sources: the Charter of the United Nations and customary international law. That law is stated in the Charter rather concisely and rather simply. However, this simplicity has given rise to problems of interpretation and application. As you know, in the Charter there are three main provisions dealing with the use of force. First there is the prohibition of the use of force in Article 2(4). Secondly there is the acknowledgement of the right of individual and collective self-defence in Article 51. Thirdly, Article 42 allows the United Nations Security Council to authorise the use of force.

I want to address three particular contributions the Court has made to the development of the law on the use of force. These three contributions are as follows:
• The contribution of the Court to the Sources of the law on the use of force;
• The contribution of the Court to the Prohibition of the Use of Force; and
• The contribution of the Court to the Law on Self-Defence.
In addressing these three contributions, I will set out what the Court has said, how the Court’s pronouncements have advanced understanding of the law in that area, and finally, how the court’s pronouncements may have found resonance in unexpected ways.


One of the Court’s primary contributions to the law on the use of force is an elucidation of the relationship between the two sources of the law on the use of force. In the Nicaragua case, the Court made clear that both sources of law—the Charter and customary international law—continue to apply, so that “States in question are bound by these rules both on the level of treaty-law and that of customary international law.”  Even if the treaty and customary rules were identical, they would “retain a separate existence.”  Indeed, the Court’s entire decision in that case was based not on the UN Charter but on customary international law. In other words, despite the centrality of the UN Charter in this area, customary international law on the use of force remains a source of rights and indeed of obligations relating to the use of force. The Court’s decision that the fact that there is a treaty dealing with a given area of international law does not mean the complete inapplicability of customary international law remains important in general international law.

The Court’s point about the abiding relevance of custom is important in the law relating to the use of force precisely because of the simplicity and concise nature of some of the provisions of the UN Charter.  For example, Article 51 acknowledges the right of self-defence but does not, in terms, set limits on that right. The Court has held that the customary international law limits of necessity and proportionality continue to apply and therefore the treaty provision and customary international law have a symbiotic relationship.

In the Nicaragua case, the Court was in the happy position of being able to find that customary international law and the UN Charter provisions on the use of force were congruent and equivalent.  However, the Court’s decision that both the treaty and custom continue to apply leaves open the possibility that custom can continue to develop, and possibly might develop in a different direction from the UN Charter. What is to happen then? How would we apply the law in such a case?

There is much discussion of the possibility that international law might include a right by States to action for humanitarian purposes. Such a right is not provided for in terms by the UN Charter. Scholars who support such a right of humanitarian intervention often point to examples of State intervention which, in their view, provide the basis for such an emerging right.  This is an argument based on the reasoning of customary international law: the argument being that there has been some practice and this is leading to a right. Those opposed to this argument argue that the instances of practice are insufficient and that in any event, there is little opinio juris (the belief in the legality of the practice) in this direction.  Again, this is an argument that there is no customary right. The Court has not explicitly pronounced on this issue, though some statements in the Nicaragua case appear sceptical of such a right.  The main point here though is that the arguments for and against appear to have proceeded on a basis assuming that there can be a customary norm of international law on humanitarian intervention. After all, the Court has said that customary international law on the use of force continues to have vitality. But if such a norm of custom were to develop how would it relate to the provisions of the UN Charter? Is it being argued that custom can supersede the UN Charter or take the law in a different dimension?

In short, the important statement of the Court that the sources of the law on the use of force are twofold is welcome and significant but it raises new important issues—of methodology and practice—that remain unresolved and unexplained.


Let us now turn to the contribution of the Court to the prohibition of the use of force. Article 2(4) of the UN Charter prohibits the threat or use of force by one State against the territorial integrity, political independence of another State or in any other manner inconsistent with the UN Charter. This is a fundamental principle of international law but there are at least two ambiguities present in the text.
• First what is the use of force and when does a State use force? Does it only relate to direct uses of force or to what extent does it cover indirect uses of force?
• Second, is the prohibition comprehensive or does it contain its own limitations? In particular do the words “force against the territorial integrity or political independence of any State” limit the prohibition only to particular types of uses of force?

The Court has had occasion to deal with the first point in the context of State support for non-State groups who use force abroad. Here the key question is what level of support by a State to a non-State group would amount to a use of force by the State and thus a breach of Article 2(4). The first point to note is that the Court has accepted that indirect uses of force amount to a breach of Article 2(4). This was done in both the Nicaragua case, where the Court said that acts which breach the principle of non-intervention and which “directly or indirectly involve the use of force, constitute a breach of the principle of non-use of force in international relations.”  This was reaffirmed in the Armed Activities case between the Democratic Republic of Congo and Uganda.

This statement by the Court is a response to the realities of international life since the drafting of the Charter. In this period, instance of State support for non-State groups which use force have increased. The Court sets out a path by which international law deals with this.

The question of what level of support amounts to a use of force in breach of Article 2(4) has been contentious. In the Nicaragua case, the Court stated that a distinction is to be drawn between the provision of weapons and logistical support, on the one hand, and the financing of non-State groups, on the other.  The former amounts to a breach of Article 2(4). However, the latter, though amounting to an unlawful intervention in internal affairs, is not a breach of Article 2(4). Although the consequences of separating out the two illegalities are still not clear, the distinction is one that has drawn some criticism. Perhaps the Court drew the distinction primarily for evidential reasons. Financial support can be used, and intended to be used, for a number of purposes, while provision of weapons and logistical support is usually clear cut.

This holding by the Court regarding indirect uses of force in State support for non-State groups is one that came to have unexpected significance earlier this year in the context of the Security Council’s authorization for the use of force in Libya.  As you will recall, questions arose as to whether the coalition using force was entitled to provide arms and other support to the then non-governmental forces in Libya. One argument used by some scholars in support of the right to provide such assistance was that since the ICJ had recognised that force may be used directly or indirectly through support to non-State groups, an authorization to use force must also contemplate indirect uses of force.


Although the right of States to act in self-defence is undenied and frequently relied upon, the scope of that right remains uncertain. As stated earlier, the Court has in many cases clarified that the right of self-defence in the Charter must be read together with the customary international law principles underpinning that right. (See the Nicaragua case, the Nuclear Weapons Advisory Opinion,  the Oil Platforms case,  and the Armed Activities case). In particular, the Charter provision, Article 51 must also be limited by the principles of necessity and proportionality. Questions remain as to how these criteria are to be interpreted and the Court has had some things to say on this. However, the Court has approached these questions of necessity and proportionality on a case by case basis without developing a general theory on how they apply.

What I really want to do here is to focus on one area where the Court has developed detailed jurisprudence. This is the question of what amounts to an armed attack which permits a response in self-defence. Article 51 states that nothing is to impair the right of self-defence if an armed attack occurs. The ICJ, in the Nicaragua case  and in subsequent cases like the Oil Platforms case has clarified that the requirement of armed attack in Article 51 is not to be equated with a use of force as stated in Article 2(4) of the Charter.  The Court has said that armed attacks are the most grave uses of force and are to be distinguished from less grave uses of force.

These decisions raises three questions:
i. Is this distinction relevant in all cases of self-defence? In particular is it relevant both in case of indirect uses of force, where a State supports a non-State group, and also in cases of direct uses of force by regular State armed forces?
ii. What are the criteria for distinguishing between uses of force that amount to an armed attack and those that do not?
iii. Are there good policy reasons to support this distinction? Does the distinction leave a State defenceless with regard to uses of force that do not amount to armed attacks?

On the first point, it is to be noted that the first case in which the Court articulated the distinction—the Nicaragua case—involved allegations of indirect force. The Court was careful to say that support for a non-State group which uses force against another can amount to an armed attack. As discussed earlier, the Court distinguished between different forms of State support to non-State groups. It held that the level of support to the non-State group affects the legal classification of the activity:

• Funding – is a breach of the norm of non-intervention, but “the Court considers that the mere supply of funds to the contras, while undoubtedly an act of intervention in the internal affairs of Nicaragua… does not in itself amount to a use of force.”
• Provision of weapons and logistical support – is an unlawful use of force. Neither amounts though to an armed attack and therefore there is no right to use force in self-defence with regard to these activities.
• However, organising and sending, by, or on behalf of, a State of an armed group could amount to an armed attack entitling the victim State to act in self-defence depending on the gravity of the force used.

While the distinction between armed attack and lesser forms of the use of force were first clarified in the context of indirect uses of force nothing in the Nicaragua case limited it to this context. Furthermore, in the Oil Platforms case, the Court has made it clear that the distinction remains valid with regard to actions of regular State forces.

What about the second question, how do we distinguish between uses of force that amount to an armed attack and those that do not? The Court has said that the distinction is one relating to the gravity of the use of force or its scale and effects. What is not clear is how we distinguish between grave uses of force from those less grave. In the Oil Platforms case, the Court did not rule out that the mining of a single military vessel, though not leading to loss of life, could be regarded as sufficiently grave.  What is also not clear is whether repeated uses of force which do not individually amount to an armed attack could, collectively, be so regarded.

This language of the Court in distinguishing uses of force on the basis of gravity, scale and effects, has found resonance in the recent amendments to the Statute of the International Criminal Court on the crime of aggression. There it is stated that an act of aggression by a State will lead to individual criminal responsibility for the crime of aggression where the act of aggression by character, gravity and scale amounts to a manifest violation of the Charter.  It remains to be seen whether the ICC will follow the interpretation of the ICJ with regard to gravity and scale.   It is not clear that the intention was to align the two standards but there are clear similarities as the same language has been used.

One final area in the law of self-defence where the Court’s jurisprudence has been influential but the subject of intense debate is the test for self-defence against non-State groups acting from abroad. As has been seen, in the Nicaragua case, the ICJ stated that a State commits an armed attack against another where it organises and sends a non-State group.  Recall that lower forms of providing support are not enough for a self-defence right to arise. In short, for self-defence to arise the act of the non-State group must be attributable to another State.

In some ways this has proven to be the most contentious aspect of the Court’s case law on the use of force. There were some criticisms of the Court’s holding at the time and challenges to it have increased in the last 10 years. It is arguable that State practice, particularly since 9/11, have taken a different turn. However, the Court has reasserted this principle that requires sending of the group for a self-defence right to arise. It has done so, over the objection of individual judges, in the Israeli Wall in Palestine Advisory Opinion  and the Armed Activities case.

As the principal judicial organ of the UN, the ICJ has some responsibility for helping to achieve the peaceful world that the Charter aims for. It does this by settling disputes and by promoting the rule of law. However, that contribution to peace is no greater than in those areas where the Court is not only called upon to do these two things but to do them in the context of the use of force.


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One Response

  1. An excellent iteration, although some others might disagree on fine points.