“Article II. The High Contracting Parties agree that the settlement or solution of all disputes or conflicts of whatever nature or whatever origin they may be, which may arise among them, shall never be sought except by pacific means.”
The question is, what was the legal effect of this Pact? The nations who signed the Pact or adhered to it unconditionally condemned recourse to war for the future as an instrument of policy, and expressly renounced it. After the signing of the Pact, any nation resorting to war as an instrument of national policy breaks the Pact. In the opinion of the Tribunal, the solemn renunciation of war as an instrument of national policy necessarily involves the proposition that such a war is illegal in international law; and that those who plan and wage such a war, with its inevitable and terrible consequences, are committing a crime in so doing. War for the solution of international controversies undertaken as an instrument of national policy certainly includes a war of aggression, and such a war is therefore outlawed by the Pact. As Mr. Henry L. Stimson, then Secretary of State of the United States, said in 1932:
“War between nations was renounced by the signatories of the Kellogg-Briand Treaty. This means that it has become throughout practically the entire world . . . an illegal thing. Hereafter, when nations engage in armed conflict, either one or both of them must be termed violators of this general treaty law . . . . We denounce them as law breakers.”
But it is argued that the Pact does not expressly enact that such wars are crimes, or set up courts to try those who make such wars. To that extent the same is true with regard to the laws of war contained in the Hague Convention. The Hague Convention of 1907 prohibited resort to certain methods of waging war. These included the inhumane treatment of prisoners, the employment of poisoned weapons, the improper use of flags of truce, and similar matters. Many of these prohibitions had been enforced long before the date of the Convention; but since 1907 they have certainly been crimes, punishable as offenses against the laws of war; yet the Hague Convention nowhere designates such practices as criminal, nor is any sentence prescribed, nor any mention made of a court to try and punish offenders. For many years past, however, military tribunals have tried and punished individuals guilty of violating the rules of land warfare laid down by this Convention. In the opinion of the Tribunal, those who wage aggressive war are doing that which is equally illegal, and of much greater moment than a breach of one of the rules of the Hague Convention. In interpreting the words of the Pact, it must be remembered that international law is not the product of an international legislature, and that such international agreements as the Pact of Paris have to deal with general principles of law, and not with administrative matters of procedure. The law of war is to be found not only in treaties, but in the customs and practices of states which gradually obtained universal recognition, and from the general principles of justice applied by jurists and practised by military courts. This law is not static, but by continual adaptation follows the needs of a changing world. Indeed, in many cases treaties do no more than express and define for more accurate reference the principles of law already existing.
The view which the Tribunal takes of the true interpretation of the Pact is supported by the international history which preceded it. In the year 1923 the draft of a Treaty of Mutual Assistance was sponsored by the League of Nations. In Article I the Treaty declared “that aggressive war is an international crime”, and that the parties would “undertake that no one of them will be guilty of its commission”. The draft treaty was submitted to 29 states, about half of whom were in favor of accepting the text. The principal objection appeared to be in the difficulty of defining the acts which would constitute “aggression”, rather than any doubt as to the criminality of aggressive war. The preamble to the League of Nations 1924 Protocol for the Pacific Settlement of International Disputes (“Geneva Protocol”), after “recognising the solidarity of the members of the international community”, declared that “a war of aggression constitutes a violation of this solidarity and is an international crime.” It went on to declare that the contracting parties were “desirous of facilitating the complete application of the system provided in the Covenant of the League of Nations for the pacific settlement of disputes between the States and of ensuring the repression of international crimes.” The Protocol was recommended to the members of the League of Nations by a unanimous resolution in the assembly of the 48 members of the League. These members included Italy and Japan, but Germany was not then a member of the League.
Although the Protocol was never ratified, it was signed by the leading statesmen of the world, representing the vast majority of the civilized states and peoples, and may be regarded as strong evidence of the intention to brand aggressive war as an international crime.
At the meeting of the Assembly of the League of Nations on 24 September 1927, all the delegations then present (including the German, the Italian, and the Japanese), unanimously adopted a declaration concerning wars of aggression. The preamble to the declaration stated:
“The Assembly:
Recognizing the solidarity which unites the community of nations;
Being inspired by a firm desire for the maintenance of general peace;