The Treaty of London was a consequential agreement reached in April 1915, marking Italy's entry into World War I as a member of the Allied Powers. The treaty negotiations involved key diplomatic figures, chiefly Italian Foreign Minister Sidney Sonnino, who sought to secure promises of territorial expansion and other benefits for Italy, which had remained neutral since the start of the war in 1914. The discussions primarily took place amidst the backdrop of shifting alliances and the desire of Italy to assert its influence in the post-war order.

Italy's war aims, as outlined in the treaty, included claims to territories inhabited by Italians, such as parts of Austria-Hungary, particularly South Tyrol, Trentino, and parts of Istria and Dalmatia. In exchange for its military commitment against the Central Powers, Italy was promised these territorial expansions, which were seen as critical to national unification and identity.

Officially signing the treaty on April 26, 1915, not only reinforced Italy's military position but also indicated a significant moment in the broader conflict, influencing the dynamics and strategies of the Allied Powers. Italy's entry swelled their ranks and presented new opportunities and challenges on the battlefield. This strategic realignment would have far-reaching implications over the course of the war, including the harsh realities faced in the mountainous fronts with Austria-Hungary, where Italy would incur heavy losses amidst challenging warfare.