The Triple Alliance was an agreement between Germany, Austria-Hungary, and Italy. It was formed on 20 May 1882 and renewed periodically until it expired in 1915 during World War I. Germany and Austria-Hungary had been closely allied since 1879. Italy was looking for support against France shortly after it lost North African ambitions to the French. Each member promised mutual support in the event of an attack by any other great power. The treaty provided that Germany and Austria-Hungary were to assist Italy if it was attacked by France without provocation. In turn, Italy would assist Germany if attacked by France. In the event of a war between Austria-Hungary and Russia, Italy promised to remain neutral. The existence and membership of the treaty were well known, but its exact provisions were kept secret until 1919.

When the treaty was renewed in February 1887, Italy gained an empty promise of German support of Italian colonial ambitions in North Africa in return for Italy's continued friendship. Austria-Hungary had to be pressured by German chancellor Otto von Bismarck into accepting the principles of consultation and mutual agreement with Italy on any territorial changes initiated in the Balkans or on the coasts and islands of the Adriatic and Aegean seas. Italy and Austria-Hungary did not overcome their basic conflict of interest in that region despite the treaty. In 1891, attempts were made to join Britain to the Triple Alliance, which, though unsuccessful, were widely believed to have succeeded in Russian diplomatic circles.Shortly after renewing the Alliance in June 1902, Italy secretly extended a similar guarantee to France. By a particular agreement, neither Austria-Hungary nor Italy would change the status quo in the Balkans without previous consultation.On 18 October 1883 Carol I of Romania, through his Prime Minister Ion C. Brătianu, had also secretly pledged to support the Triple Alliance, but he later remained neutral in the First World War due to viewing Austria-Hungary as the aggressor. On 1 November 1902, five months after the Triple Alliance was renewed, Italy reached an understanding with France that each would remain neutral in the event of an attack on the other.

When Austria-Hungary found itself at war in August 1914 with the rival Triple Entente, Italy proclaimed its neutrality, considering Austria-Hungary the aggressor. Italy also defaulted on the obligation to consult and agree to compensations before changing the status quo in the Balkans, as agreed in 1912 renewal of the Triple Alliance. Following parallel negotiation with both Triple Alliance (which aimed to keep Italy neutral) and the Triple Entente (which aimed to make Italy enter the conflict), Italy sided with the Triple Entente and declared war on Austria-Hungary.