The Dual Alliance of 1879 between Austria-Hungary and Germany:
Should … one of the two Empires be attacked by Russia, the Parties are bound to come to the assistance one of the other with the whole war strength of their Empires, and accordingly only to conclude peace together and upon mutual agreement.
Should one of the Parties be attacked by another Power, the other Party binds itself hereby, not only not to support the aggressor against its allly, but to observe at least a benevolent neutral attitude towards its fellow Party.
The duration of this Treaty shall be provisionally fixed at five years from the day of ratification. One year before the expiration of this period the two Parties shall consult together concerning the question whether the conditions serving as the basis of the Treaty still prevail, and reach an agreement in regard to the further continuance or possible modification. If in the course of the first month of the last year of the Treaty no invitation has been received from either side to open these negotiations, the Treaty shall be considered as renewed for a further period of three years.
This Treaty shall, in conformity with its peaceful character, and to avoid any misinterpretation, be kept secret by the two Parties, and only communicated to a third Power upon a joint understanding between the two Parties, and according to the terms of a special Agreement.