The Triple Alliance was the treaty by which Germany, Austria-Hungary and Italy pledged (May 20, 1882) to support each other militarily in the event of an attack against any of them by two or more great powers. Germany and Italy additionally undertook to support one another in the event of attack by France. In a supplementary declaration, however, Italy specified that her undertakings could not be regarded as being directed against the United Kingdom. Shortly after renewing the Alliance in June 1902, Italy secretly extended a similar guarantee to France, effectively nullifying her part in the alliance.

Italy's partial adherence to the German-Austrian Dual Alliance was triggered partly by anger at France's May 1881 seizure of Tunisia, which many Italians had seen as a potential colony. But Italian public opinion remained unenthusiastic about their country's alignment with Austria-Hungary, a past enemy of Italian unification (1820-21, 1848-49, 1859, 1866) whose Italian-majority districts in the Trentino and Istria were seen as Italia irredenta ("unredeemed Italy"). When Germany and Austria-Hungary found themselves at war in August 1914 with the rival Triple Entente of Britain, France and the latter's ally Russia, Italy declared neutrality, subsequently entering the conflict on the side of the Entente against Austria-Hungary in May 1915 and Germany in August 1916 (see World War I) and gaining most of the Austrian territories she had coveted at the peace settlement of 1919.