The Treaty of Rapallo was an agreement between the Kingdom of Italy and the Kingdom of Serbs, Croats and Slovenes in the aftermath of the First World War. It was intended to settle the Adriatic question, which referred to Italian claims over territories promised to the country in return for its entry into the war against Austria-Hungary, claims that were made on the basis of the 1915 Treaty of London. The wartime pact promised Italy large areas of the eastern Adriatic. The treaty, signed on 12 November 1920 in Rapallo, Italy, generally redeemed the promises of territorial gains in the former Austrian Littoral by awarding Italy territories generally corresponding to the peninsula of Istria and the former Princely County of Gorizia and Gradisca, with the addition of the Snežnik Plateau, in addition to what was promised by the London treaty. The articles regarding Dalmatia were largely ignored. Instead, in Dalmatia, Italy received the city of Zadar and several islands. Other provisions of the treaty contained safeguards for the rights of Italian nationals remaining in the Kingdom of Serbs, Croats and Slovenes, and provisions for commissions to demarcate the new border, and facilitate economic and educational cooperation. The treaty also established the Free State of Fiume, the city-state consisting of the former Austro-Hungarian Corpus separatum that consisted of Rijeka and a strip of coast giving the new state a land border with Italy at Istria.

The Kingdom of Italy was a state that existed from 17 March 1861, when Victor Emmanuel II of Sardinia was proclaimed King of Italy, until 12 June 1946, when the monarchy was abolished, following civil discontent that led to an institutional referendum on 2 June 1946, which resulted in a modern Italian Republic. The kingdom was established through the unification of several states over a decades-long process, called the Risorgimento. That process was influenced by the Savoy-led Kingdom of Sardinia, which can be considered Italy's legal predecessor state.