§ 503. Such obligation as is inconsistent with obligations under treaties previously concluded by one State with another cannot be the object of a treaty with a third State. Thus, in 1878, when after the war Russia and Turkey concluded the preliminary Treaty of Peace of San Stefano, which was inconsistent with the Treaty of Paris of 1856 and the Convention of London of 1871, England protested,[862] and the Powers met at the Congress of Berlin to arrange matters by mutual consent.
[862] See Martens, N.R.G. 2nd Ser. III. p. 257.
Object must be physically possible.
§ 504. An obligation to perform a physical impossibility[863] cannot be the object of a treaty. If perchance a State entered into a convention stipulating an obligation of that kind, no right to claim damages for non-fulfilment of the obligation would arise for the other party, such treaty being legally null and void.
Immoral Obligations.
§ 505. It is a customarily recognised rule of the Law of Nations that immoral obligations cannot be the object of an international treaty. Thus, an alliance for the purpose of attacking a third State without provocation is from the beginning not binding. It cannot be denied that in the past many treaties stipulating immoral obligations have been concluded and executed, but this does not alter the fact that such treaties were legally not binding upon the contracting parties. It must, however, be taken into consideration that the question as to what is immoral is often controversial. An obligation which is considered immoral by other States may not necessarily appear immoral to the contracting parties, and there is no Court that can decide the controversy.
Illegal Obligations.
§ 506. It is a unanimously recognised customary rule of International Law that obligations which are at variance with universally recognised principles of International Law cannot be the object of a treaty. If, for instance, a State entered into a convention with another State not to interfere in case the latter should appropriate a certain part of the Open Sea, or should command its vessels to commit piratical acts on the Open Sea, such treaty would be null and void, because it is a principle of International Law that no part of the Open Sea can be appropriated, and that it is the duty of every State to interdict to its vessels the commission of piracy on the High Seas.