Emer De Vattel, ‘Of Treaties Of Alliance, And Other Public Treaties’ in Emer De Vattel, The Law of Nations (Translated by Joseph Chitty, with additional notes and references by Edward D. Ingraham. Philadelphia,T. & J.W. Johnson, Law Booksellers, 1853) pp. 192-212.
Emer de Vattel (1714-1767) is considered one of the founding fathers of modern international law. He taught in Neuchâtel, which at the time was part of Preussia, and thus close to international borders and daily international discourse with sovereign Swiss cantons. He is informed by practical needs and treaty interpretation guided to preserve freedom of States from interference and protection of their autonomous will. On Vattel’s main work, ‘The Law of Nations; or, Principles of the Law of Nature, applied to the Conduct and Affairs of Nations and Sovereigns’, Martti Koskenniemi writes in From Apology to Utopia: The Structure of International Legal Argument (Cambridge: Cambridge University Press, 2005) pp. 112; 117-118 (footnotes omitted):
Growing directly out of the ideological environment of the Enlightenment, Vattel’s work was purged from Christian morality and theological authorities. It was a “realistic” book, especially useful for diplomats and practitioners, not least because it seemed to offer such compelling rhetorics for the justification of most varied kinds of State action.
Vattel’s professed programme is to concretize Wolff’s abstract theories for the use of sovereigns to whom he expressly writes. His concern is to overcome the utopian nature of his predecessors’ work, identified with their excessive use of abstract deductions from general principles.
Instead, he defends his views by referring to contemporary State practice. The identity of his work lies in the idealism/realism distinction which is transformed therein into the all-important differentiations between necessary and voluntary law and internal and external duties.
Treaties, for example, are in principle sacred and the one who violates them violates the natural law of nations. However, treaties which conflict with the State’s duty towards itself and treaties which are “pernicious” are void. The conflicting or pernicious nature of the treaty is left for each State’s own evaluation. Thus the risk arises that the State remains bound only if that is what it wills. Vattel attempts to mitigate this threat by two constructions. In the first place, this exception is treated as an implied condition in the treaty. Non-observance in case of the treaty’s conflicting or pernicious nature is based on the treaty and thus on the other party’s consent as well.
In the second place, the potential conflict between the treaty’s objectively binding nature and the State’s freedom is referred away from discourse, into conscience. There remains the imperfect duty of the State to interpret treaties equitably and in good faith.
Vattel’s discourse creates a potential for conflict between private morality (imperfect duty) and public law which could not arise under early doctrine. The suggested resolution takes place within conscience. The unsaid assumption is that States do act in good faith. Once that assumption is questioned, the system appears apologist. For Vattel, however, the assumption seems justifiable considering that the law is, by definition, based on the State’s duties towards itself. Obligations have reality because fulfilling them is assumed to be in the State’s own self interest.
The chapter is from the second book of Emer De Vattel’s The Law of Nations entitled ‘of treaties of alliance, and other public treaties’. Vattel provides an overview regarding the entering of treaties between states, the rules for honouring such treaties and the different forms these treaties may take. In Vattel’s view treaties are made between nations in order to secure advantages that would be bestowed upon them by natural law but cannot be ensured in a world of unreliable states. A treaty is defined as a standalone act made by the sovereign or a proxy, in the name of the state, and is intended to be for the public good. Although the sovereign has the power to make and ratify treaties they may be constrained by other bodies depending on the individual state. Equally these bodies may enter into treaties themselves independent of the sovereign.
Vattel identifies several factors that should constrain a state from entering into certain types of treaties: for example a state should never enter a treaty that contradicts other treaties that are in place, nor is a treaty valid that threatens the survival of a nation or is unjust or dishonest. He rejects religious differences as a reason not to enter a treaty with a state unless the religion violates the laws of nature. In Vattel’s view a treaty constitutes a perfect promise meaning that any violation is a violation of natural law. The honouring of promises is essential to peace and security as much as between nations a between men. When honouring treaties a state should always prioritise its own survival and then, if unable to fulfil all obligations, the treaty that has been in place longest.
Finally, Vattel discusses the nature of treaties and distinguishes between equal alliances, where the actors are equal and equal treaties where each partner commits to the same thing. Where a treaty can be unequal the alliance can still be equal, for example if a stronger party commits to more than a weaker one. Where the weaker party has more obligations Vattel sees the alliance as always being unequal. These unequal alliances impair sovereignty when any rights of a nation are ceded to an ally or the use of them dependent on that ally. In addition treaties can be distinguished between personal and real alliances. Personal alliances expired at the death or end of the reign of one of those who contracted the alliance. A real alliance on the other hand is attached to the body of the state and lasts as long as prescribed. An alliance made by a republic is real and continues even if the institutions of the state change.
You can find a scan (PDF) of the original text here: De Vattel – The Law of Nations