The really vital question is as to the effect of the Protocol and of the Covenant upon non-Members of the League in their relations with Signatories to the Protocol.
Even assuming that the plans now proposed for the admission of Germany to the League are carried out, there will remain for a considerable period two Great Powers, the United States and Russia, outside the League; and there are two other States of occasional international importance, the admission of which to the League is not, so far as I know, presently contemplated, these being Mexico and Egypt.
Accordingly, the possible effect of the Covenant and the Protocol on non-Members of the League is one of very great consequence. It is a question which is being actively discussed in so far as it may have a bearing on the relations between Great Britain and the United States.
It is unquestionably true that the Protocol may have a real effect on non-Members of the League. Of course there is a legal formula which correctly says that a treaty cannot bind States not parties thereto, res inter alios acta; but even in the strictest legal sense this formula is only part of the truth in international matters. Any one who questions this will be convinced by reading Roxburgh's International Conventions and Third States.[[2]] A treaty between State A and State B may harm State C or it may benefit State C, as the Treaty of Versailles benefited Denmark by the cession of Slesvig, though Denmark was a neutral and not a party to the Treaty of Peace.[[3]]
Let us consider the matter first from the point of view of the Covenant. There are sanctions which may be applied under the Covenant and the application of these sanctions might affect a non-Member of the League either because they were applied against that particular non-Member or because they were applied against some other State.
It is rather curious that this question has not been very much considered under the Covenant; interest in it has been greatly revived by the Protocol; but the possible realities under the Covenant are, it seems to me, in some respects more important than those under the Protocol alone.
In considering this question it is well to look at it from the concrete point of view with a specific instance or example before us.
The sanctions of the Covenant[[4]] are an economic and financial blockade. These sanctions may be applied either as against a Member of the League which resorts to war contrary to the provisions of the Covenant or they may be applied against a non-Member of the League which resorts to war against a Member after refusing to settle its dispute with that Member (Covenant, Article 17, paragraph 3).
Suppose at the time of the Corfu dispute, Italy had gone on to war against Greece, and the British had deemed it their duty to apply an economic blockade against Italy.