Yugoslav Committee in the context of "Frano Supilo"

Yugoslavism, Yugoslavdom, or Yugoslav nationalism is an ideology supporting the notion that the South Slavs, namely the Bosniaks, Bulgarians, Croats, Macedonians, Montenegrins, Serbs, and Slovenes, belong to a single Yugoslav nation separated by diverging historical circumstances, forms of speech, and religious divides. During the interwar period, Yugoslavism became predominant in, and then the official ideology of, the Kingdom of Yugoslavia. There were two major forms of Yugoslavism in the period, the first of which is the regime-favoured integral Yugoslavism, promoting unitarism, centralisation, and unification of the country's ethnic groups into a single Yugoslav nation, by coercion if necessary. The approach was also applied to languages spoken in the Kingdom. The main alternative was federalist Yugoslavism, which advocated the autonomy of the historical lands in the form of a federation and gradual unification without outside pressure. Both agreed on the concept of National Oneness developed as an expression of the strategic alliance of South Slavs in Austria-Hungary in the early 20th century. The concept was meant as a notion that the South Slavs belong to a single "race", were of "one blood", and had shared language. It was considered neutral regarding the choice of centralism or federalism.

The Yugoslavist idea has roots in the 1830s Illyrian movement in Habsburg Croatia, where a group of intellectuals saw the unity of South Slavs within the Austrian Empire or outside of it as a protection against Germanisation and Magyarisation. Cooperative talks began with Serbian politicians and working to standardise Serbo-Croatian as a common language with orthographer Vuk Karadžić, with limited success. Following the Austro-Hungarian Compromise of 1867, the concept was rivalled by Trialism. Control of the Balkans by the Ottoman Empire and Austria-Hungary prevented practical implementation of Yugoslavist ideas until the Ottomans were pushed out of the Balkans in the 1912 First Balkan War and Austria-Hungary disintegrated in the final days of the First World War. During the war, preparations for unification began in the form of the Niš Declaration of Serbian war aims, the establishment of the Yugoslav Committee to represent South Slavs living in Austria-Hungary, and the adoption of the Corfu Declaration on principles of unification. The short-lived State of Slovenes, Croats and Serbs was proclaimed in the South Slavic lands formerly ruled by the Habsburgs at the end of the First World War. Its leadership primarily wanted unification with Serbia on a federal basis, while Serbia preferred a centralised state.

The State of Slovenes, Croats and Serbs became merged with the Kingdom of Serbia and the Kingdom of Montenegro to form the nation of Yugoslavia in 1918. The formation of Yugoslavia began with the formation of the Yugoslav Committee, a collection of mostly Croats, then Serbs and later Slovenes, whose goal was to form a single south Slavic state. In October 1918 the Croatian Parliament declared the Kingdom of Croatia-Slavonia as an independent state, which, in December that same year, incorporated into the State of Slovenes, Croats and Serbs, merged with Kingdom of Serbia and Kingdom of Montenegro and created the Kingdom of Serbs, Croats and Slovenes. The kingdom would be renamed to Yugoslavia in 1929, and ruled by Serbian Karađorđević dynasty till Second World War. After the formation of Yugoslavia, Serbia attempted to create a "Greater Serbia" by using police intimidation and vote rigging to establish a Serbian controlled Yugoslavia. From 1929-1941 Serbian controlled Yugoslavia established control over Croatia through Royal Yugoslav police force brutality and assassinations of important Croatians.

The Niš Declaration (Serbian: Niška deklaracija, Serbian Cyrillic: Нишка декларација) was a document issued on 7 December 1914, in the midst of World War I, in which the government of the Kingdom of Serbia formally declared its wartime objectives. Published during the Battle of Kolubara as a defensive declaration seeking to attract support from the South Slavs living in Austria-Hungary, it contained a promise to work for the liberation of South Slavs from foreign rule and the establishment of a common South Slavic state after the war. As the Serbian government had withdrawn from Belgrade earlier in the conflict, the declaration was adopted in the temporary Serbian capital of Niš.

The Triple Entente did not accept the objectives set out in the Niš Declaration because they supported the preservation of Austria-Hungary. In subsequent years, Allied support for a separate peace with Austria-Hungary and trialist reform proposals such as the May Declaration of 1917 motivated the Serbian government to cooperate with the Yugoslav Committee. Negotiations between the Serbian government and the Yugoslav Committee led to the Corfu Declaration of 1917, in which the two sides agreed to the creation of a common South Slavic state once the war had ended.

The Corfu Declaration (Serbo-Croatian: Krfska deklaracija, Крфска декларација) was an agreement between the prime minister of Serbia, Nikola Pašić, and the president of the Yugoslav Committee, Ante Trumbić, concluded on the Greek island of Corfu on 20 July 1917. Its purpose was to establish the method of unifying a future common state of the South Slavs living in Serbia, Montenegro and Austria-Hungary after the First World War. Russia's decision to withdraw diplomatic support for Serbia following the February Revolution, as well as the Yugoslav Committee's sidelining by the trialist reform initiatives launched in Austria-Hungary, motivated both sides to attempt to reach an agreement.

Pašić and Trumbić's positions were disparate. Pašić advocated for a centralist government, while Trumbić argued for a federal state, leaving significant powers to federal units and safeguarding national rights. The resulting declaration glossed over the matter of the system of government. As a compromise, it specified only that the common Kingdom of Serbs, Croats and Slovenes would be a constitutional monarchy ruled by the currently reigning Serbian Karađorđević dynasty, deferring most questions to a future Constitutional Assembly. During the discussions, which lasted 35 days, Trumbić had little support for his view from the other members of the Yugoslav Committee, who were preoccupied with the threat posed by Italy, which had been promised territory under the 1915 Treaty of London.

The May Declaration (Slovene: Majniška deklaracija, Croatian: Svibanjska deklaracija, Serbian: Majska deklaracija/Мајска декларација) was a manifesto of political demands for unification of South Slav-inhabited territories within Austria-Hungary put forward to the Imperial Council in Vienna on 30 May 1917. It was authored by Anton Korošec, the leader of the Slovene People's Party. The document was signed by Korošec and thirty-two other council delegates representing South-Slavic lands within the Cisleithanian part of the dual monarchy – the Slovene Lands, the Dalmatia, Istria, and the Condominium of Bosnia and Herzegovina. The delegates who signed the declaration were known as the Yugoslav Club.

The May Declaration was generally favourably greeted by Croat politicians in Croatia-Slavonia, but was met with opposition or indifference by the Bosniaks, the Bosnian Serbs, and the Croatian Serbs. The declaration also applied pressure on the government of the Kingdom of Serbia which saw the objectives of the declaration as a threat to fulfilment of its First World War goals in terms of territorial expansion. This led the Kingdom of Serbia government to give priority to the drafting of the Corfu Declaration, with the Yugoslav Committee outlining the principles of unification of a common state for all South Slavs living in Austria-Hungary, Serbia, and Montenegro at the time. The advocation of the May Declaration was banned by Austro-Hungarian authorities in May 1918.