In the aftermath of the First World War, the Adriatic question or Adriatic problem concerned the fate of the territories along the eastern coast of the Adriatic Sea that formerly belonged to the Austro-Hungarian Empire. The roots of the dispute lay in the secret Treaty of London, signed during the war (26 April 1915), and in growing nationalism, especially Italian irredentism and Yugoslavism, which led ultimately to the creation of Yugoslavia. The question was a major barrier to agreement at the Paris Peace Conference, but was partially resolved by the Treaty of Rapallo between Italy and Yugoslavia on 12 November 1920.
Background
Austria-Hungary exited the war on 3 November 1918, when it ordered its troops to cease fighting. The Armistice of Villa Giusti, signed with Italy that day, took effect on 4 November, and on 13 November the Armistice of Belgrade was signed with Italy's allies on the Balkan front. Italy began immediately to occupy territories ceded to it by the treaty of 1915, while simultaneously the South Slavs formed local governments in opposition to both Italian expansion and Austro-Hungarian authority. A National Council of Slovenes, Croats and Serbs was set up in Zagreb on 5–6 October, and the State of Slovenes, Croats and Serbs was proclaimed there on 29 October and that same day the Sabor, the legitimate parliament of Croatia-Slavonia, declared independence from Austria-Hungary. On 1 December the Kingdom of Serbs, Croats and Slovenes (later Yugoslavia) was formed in Belgrade by union of this new state with Serbia and Montenegro.
Arguments
Populations
The main argument presented by Yugoslavia was that the territories under consideration contained about seven million Slavs, almost the entire population.
Of the Dalmatian islands, only Lošinj (Lussin) had an Italian majority. When the hinterland of Fiume was included along with its suburbs the Yugoslav majority increased further. The Italian claim on Gorizia and Gradisca was generally recognised, as was its claim on the Slavic settlements around Friuli.
At the Congress of Oppressed Nationalities of the Austro-Hungarian Empire in Rome (8–10 April 1918), Italy lent official support to the Declaration of Corfu (20 July 1917), a Yugoslavist document supported by Britain and France that expressed the need to unite the South Slavs politically.
Geography
The Italians argued that the natural geographic boundary of Italy included the Julian and Dinaric Alps, and that therefore the Austro-Hungarian littoral lay within geographic Italy. The strategic importance of the geography of the eastern coast of the Adriatic has been generally accepted. The Chief of the Division of Boundary Geography with the American delegation to the Paris Peace Conference, Douglas Wilson Johnson, wrote at the time, "Any naval power on the [Adriatic] eastern coast must find itself possessing immense advantages over Italy." Johnson went on to note that the offer of Pula (Pola), Vlorë (Valona) and a central Dalmatian island group to the Italians effectively settled the strategic problem and balanced the two Adriatic powers.
Allied occupation
Joint occupation of Fiume
On 29 October 1918 the Austro-Hungarians evacuated Fiume, and the new Croatian mayor, Rikard Lenac, proclaimed the town's adherence to the National Council of the State of Slovenes, Croats and Serbs. On 30 October the Italian community set up a "national council" headed by Antonio Grossich and proclaimed Fiume's union with Italy. The next day the local governor handed over power to the Italians, as did the governor of Trieste. On 4 November an Italian naval detachment under Admiral Guglielmo Rainer aboard the battleship arrived in the harbour of Fiume. Rainer declared the local government dissolved and, on 14 November Italian Prime Minister Vittorio Orlando, acting on the advice of Chief of Staff Armando Diaz, ordered Rainer to land a troop of marines. The next day (15 November) Diaz requested that Allied troops take part in the occupation of Fiume. The commander of British forces on the Italian Front, the Earl of Cavan, was ordered to send a company "to show that the occupation is allied, and to keep order". That same day 2,000 Serbian soldiers arrived on the outskirts of Fiume.