Defining International Aggression
The Search for World Peace


Commentary on the Definition of a Case of Aggression.

Drawn up by a Special Committee of the Temporary Mixed Commission |1|.

1. It would be theoretically desirable to set down in writing, if it could be done, an exact definition of what constitutes an act of aggression. If such a definition could be drawn up, it would then merely remain for the Council to decide in each given case whether an act of aggression within the meaning of this definition had been committed.

It appears, however, to be exceedingly difficult to draw up any such definition. In the words of the Permanent Advisory Commission, "under the conditions of modern warfare, it would seem impossible to decide even in theory what constitutes an act of aggression".

2. Hitherto, according to the opinion expressed by certain members of the Permanent Advisory Comission, in the report drawn up by that Commission, "aggression could be defined as mobilisation or the violation of a frontier. This double test has lost its value".

It is further stated that:

    "Mobilisation, which consisted, until quite recently, of a few comparatively simple operations (calling up of reserves, purchases or requisitions and establishment of war industries, after the calling-up of the men), has become infinitely more complicated and more difficult both to discover at its origin and to follow in its development. In future, mobilisation will apply not merely to the army but to the whole country before the outbreak of hostilities (collection of stocks of raw materials and munitions of war, industrial mobilisation, establishment or increased output of industries). All these measures, which give evidence of an intention to go to war, may lead to discussions and to conflicting interpretations, thus securing decisive advantages to the aggressor unless action be taken."

3. Similarly, in the view of the Permanent Advisory Commission, the test of the violation of a frontier has also lost its value.

The report states:

    "The violation of a frontier by 'armed forces' will not necessarily be, in future such an obvious act of violence as it has hitherto been... The passage of the frontier by the troops of another country does not always mean that the latter country is the aggressor. Particularly in the case of small States, the object of such action may be to establish an initial position which shall be as advantageous as possible for the defending country, and to do so before the adversary has had time to mass his superior forces. A military offensive of as rapid a character as possible may therefore be a means, and perhaps the only means, whereby the weaker party can defend itself against the stronger. It is also conceivable that a small nation might be compelled to make use of its air forces in order to forestall the superior forces of the enemy and take what advantage was possible from such action.

    "Finally, the hostilities between two naval Powers generally begin on sea by the capture of merchant vessels or other acts of violence – very possibly on the high seas outside territorial waters. The same applies to air operations which may take place without any violation of the air frontiers of States."

Nevertheless it is still conceivable that in many cases the invasion of a territory constitutes an act of aggression and, in any case, it is important to determine which State had violated the frontier.

If the troops of one Power invade the territory of another, this fact in itself constitutes a presumption that the first Power has committed a wrongful act of aggression.

But, apart from the considerations already given, this is not entirely conclusive. When armies have been practically in contact on the frontier which divides their respective countries, it may be exceedingly difficult to obtain conclusive evidence as to which of them first crossed the frontier; and, once the frontier is crossed and hostilities have begun, it may not be possible to know from the geographical position of the troops alone which State was guilty.

4. In order to avoid such a case arising, the Council might desire, in certain cases where such a course could be followed without disadvantage to either party, either before hostilities began or even after they had begun, to invite both parties to withdraw their troops a certain distance behind a given line. It might be that such a request could be made by the Council with the intimation that, if either party refused to accede to it, such refusal would be considered as an element in deciding which was the aggressor |2|.

5. There may, of course, be other cases in which some action of one of the parties will simplify the matter by proving it clearly to be the aggressor. Jf, for example, one Power carried out a large-scale attack upon the territory of the other, that would be conclusive. Similarly, a surprise attack by poison gas, executed from the air on the territory of the other party, would be decisive evidence.

6. It may, however, be accepted that no satisfactory definition of what constitutes an act of aggression could be drawn up. But even supposing that. such a definition were possible, there would still be difficulty in determining when an act of aggression within the meaning of this definition has actually taken place. In the view of the Permanent Advisory Commission, the signs of an intention of aggression would appear in the following order:

    (1) Organisation on paper of industrial mobilisation.
    (2) Actual organisation of industrial mobilisation.
    (3) Collection of stocks of raw materials.
    (4) Setting on foot of war industries.
    (5) Preparation for military mobilisation.
    (6) Actual military mobilisation.
    (7) Hostilities.

    Numbers (1) and (5) (and to some extent Number (2)), which are in allc ases difficult to recognise, may, in those countries which are not subject under the Peace Treaties to any obligation to disarm, represent precaution which every Government is entitled to take.

    Number (3) may be justified by economic reasons, such as profiting by advantageous markets or collecting stocks in order to guard against the possible closing of certain channels of supply owing to strikes, etc.

    Number (4) (Setting on foot of war industries) is the first which may be definitely taken as showing an intention to commit aggression: it will, however, be easy to conceal this measure for a long period in countries which are under no military supervision.

    When Numbers (6) and (7) are known to have taken place, it is too late.

    In the absence of any indisputable test, Governments can only judge by an impression based upon the most various factors, such as:

    The political attitude of the possible aggressor:
    His propaganda;
    The attitude of his press and population;
    His policy on the international market, etc.

7. One of the conclusions which follows from the above contentions set forth in the report of the Permanent Advisory Commission is that, quite apart from the material sides of the aggressive intention, the real act of aggression may lie not so much in orders given to its troops by one of the parties as in the attitude which it adopts in the negotiations concerning the subjects of dispute. Indeed, it might be that the real aggression lies in the political policy pursued by one of the parties towards the other. For this reason it might perhaps appear to the Council that the most appropriate measure that could be taken would be to invite the two parties either to abstain from hostilities or to cease the hostilities they have begun, and to submit their whole dispute to the recommendation of the Council or the decision of the Permanent Court of International Justice, and to undertake to accept and execute whatever recommendation or decision either of these bodies might give. Such an invitation might again be accompanied by an intimation that the party which refused would be considered to be the aggressor.

8. It is clear, therefore, that no simple definition of aggression can be drawn up, and that no simple test of when an act of aggression has actually taken place can be devised. It is therefore clearly necessary to leave the Council complete discretion in the matter, merely indicating that the various factors mentioned above may provide the elements of a just decision.

These factors may be summarised as follows:

    (a) Actual industrial and economic mobilisation carried out by a State cither in it, own territory or by persons or societies on foreign territory.

    (b) Secret military mobilisation by the formation and employment of irregular troops or by a declaration of a state of danger of war which would serve as a pretext for commencing hostilities.

    (c) Air, chemical or naval attack carried out by one party against another.

    (d) The presence of the armed forces of one party in the territory of another.

    (e) Refusal of either of the parties to withdraw their armed forces behind a line or lines indicated by the Council.

    (f) A definitely aggressive policy by one of the parties towards the other, and the consequent refusal of that party to submit the subject in dispute to the recommendation of the Council or to the decision of the Permanent Court of International Justice and to accept the recommendation or decision when given.

9. In conclusion, it may be pointed out that in the case of a surprise attack it would be relalively easy to decide on the aggressor, but that in the general case, where aggression is preceded by a period of political tension and general mobilisation, the determination of the aggressor and the moment at which aggression occurred would prove very difficult.

But it must be remembered that in such a case the Council, under the provisions of the Covenant, will have been engaged in efforts to avoid war and may therefore probably be in a position to form an opinion as to which of the parties is really actuated by aggressive intentions.


1. This Committee was composed as follows:
Lord Robert Cecil (Chairman), Count Bonin-Longare, M. Janssen, M. Jouhaux, Rear-Admiral Kiyokawa, Colonel Lobner, Admiral Marquis de Magaz, General de Marinis Stendardo di Ricigliano, Lieut.-Colonel Rtquin, Rear-Admiral Segrave. [Back]

2. Count Bonin-Longare and General de Marinis state that they would prefer that this article should be suppressed.
M. Jouhaux prefers the original text, which runs as follows: " In order to avoid such a case arising, it might well be that the Council of the League might desire, either before hostilities began or even after they had begun, to invite both parties to withdraw their troops to a certain distance behind a given line. It might be that such a request could be made by the Council with the intimation that whichever party refused to accede to it would be considered the aggressor". [Back]

Source: League of Nations, Commentary on the Definition of a Case of Aggression, Records of the Fourth Assembly, Minutes of the Third Committee, League of Nations Official Journal (Special Supplement No.16), 1923, pp. 183-185.
Editorial Note: This is a true copy of the above-referenced original document. This document is reproduced in Benjamin B. Ferencz's work "Defining International Aggression - The Search for World Peace", Vol. 1, as Document No. 2 (c).

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Published online by Equipo Nizkor - 26 March 2013