The Declaration of Corfu on 20 July 1917 was an agreement on the establishment of a united Kingdom of Serbs, Croats and Slovenes under the rule of Karadjordjević Dynasty. It was signed at Corfu against the backdrop of the First World War by the Serbian Foreign Minister Nikola Pašić and Ante Trumbić, the chairman of the Yugoslav Committee, a company founded in exile union of South Slav politicians of the Habsburg monarchy. The Entente powers, Britain and France supported the statement, while Russia has had no impact on the negotiations because of the February Revolution.
The state to be formed should have 12 million inhabitants in the area of the majority of South Slavs inhabited parts of the Habsburg Empire and still occupied by the Central Powers Kingdom of Serbia. Agreements on border demarcation with Italy had been taken already in the Treaty of London in 1915. In addition to the election of a constitutional assembly in general, equal and free elections, equality before the law, ethnic and linguistic equality and freedom of religion were provided. The form of government should be established in the adoption of the Constitution.
The proclamation of the Kingdom took place on December 1, 1918 in Belgrade by the Prince Regent Alexander. On the same day the National Assembly of Montenegro declared the accession of their country. Yugoslav representatives participated in the Paris Peace Conference in 1919, was in negotiations over the territory of the state. Among other things, Macedonia was annexed to the State. The first constitution, known as Vidovdan Constitution was announced on 28 June 1921.