Duhaime's Law Dictionary

Alliance Definition:

A military treaty between two or more states, providing for a mutually-planned offensive, or for assistance in the case of attack on any member.

The 1955, eighth edition of Oppenheim's International Law (edited by Lauterpacht) defines alliance as follows:

"Alliances, in the strictest sense of the term, are treaties of union between two or more states, for the purposes of defending each other against an attack in war, or of jointly attacking third states, or for both purposes.

"The term alliance is, however, often used in a wider sense and it comprises in such cases, treaties of union for various purposes....

"Subjects of alliances are said to be full sovereign states only....

"[A]n alliance may be offensive or defensive, or both. All three kinds may be either general alliances, in which case the allies are united against any possible enemy whatever, or particular appliances against one or more particular enemies. Alliances, further, may be either permanent or temporary; in the latter case, they expire at the end of the period of time for which they were concluded."


  • Duhaime.org, Legal Definition of Casus Foederis
  • Oppenheim, L., International Law: A Treatise, 8th Ed., Vol. 1, edited by H. Lauterpacht (New York: Longmans, Green & Co., 1955), pages 959-961

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