The occupation was intended to resolve a number of issues, including the disposal of assets of the Austro-Hungarian Navy and settlement of Italian territorial claims on the eastern coast of the Adriatic Sea.

The reasons for the occupation were addressed by the transfer of the remaining Austro-Hungarian naval assets to Italy and the Kingdom of Serbs, Croats and Slovenes, and by the 1920 Treaty of Rapallo that determined the border between the two countries.

[1] Following the 3 November 1918 Armistice of Villa Giusti, the Austro-Hungarian surrender,[2] Italian troops moved to occupy parts of the eastern Adriatic shore that had been promised to Italy under the Treaty of London, ahead of the Paris Peace Conference.

[3] The State of Slovenes, Croats and Serbs, that was carved from areas of Austria-Hungary populated by the South Slavs, authorised the Yugoslav Committee to represent it abroad,[4] and the short-lived state, which would soon seek union with the Kingdom of Serbia to establish the Kingdom of Serbs, Croats and Slovenes, laid a competing claim to the eastern Adriatic to counter Italian demands.

[8] The British and the French governments would not publicly endorse any claims exceeding those the treaty afforded while privately believing Italy deserved little because of its reserved attitude towards Germany in early stages of the war.

[10] Wilson deemed the Treaty of London a symbol of perfidy of European diplomacy[11] and held it invalid by application of the legal doctrine of clausula rebus sic stantibus due to fundamental changes of circumstances following the dissolution of Austria-Hungary.

It was intended to manage peacekeeping, normalisation of civilian life and maritime transport, distribution of the Austro-Hungarian fleet and other related issues the Paris Peace Conference had permanently settled.

Italy had already established a firm foothold in the claimed area by the time the zones were defined in Venice on 16 November in a meeting of the Adriatic Commission that was chaired by Admiral Paolo Thaon di Revel.

[18] Military authority in Rijeka and Sušak was assumed by Lieutenant Colonel Petar Teslić, who commanded eight battalions of the 79th Infantry Regiment of the former Austro-Hungarian Common Army normally based in Otočac, and National Guard volunteers, largely consisting of high-school pupils.

[26] The Italian navy arrived in the Port of Rijeka on 4 November;[19] the first group consisted of the battleship Emanuele Filiberto; and the destroyers Francesco Stocco, Vincenzo Giordano Orsini, and Giuseppe Sirtori.

[30] Some sources say Maksimović's withdrawal from the city was negotiated and made in exchange for the promise San Marzano's troops would not enter Rijeka[28] but would remain in nearby Opatija.

[31] Although neither Rijeka nor Sušak were awarded to Italy under the Treaty of London, Italian authorities justified the deployment by referring to provisions of the armistice allowing occupation of additional territories required for strategic purposes.

The commission recommended disbanding Legione "Fiumana" and reducing the number of Italian troops in the area to a single battalion as quickly as possible, leaving law enforcement to the British and the US forces.

The Italian foreign minister Tommaso Tittoni agreed with the British and French that Rijeka should be a free city under the League of Nations, and that the entirety of Dalmatia should belong to the Kingdom of Serbs, Croats and Slovenes.

[36] On 4 November 1918, three Regia Marina ships set sail from Venice to Zadar, each carrying a platoon of the Arezzo Infantry Brigade to enforce the Italian claim against the city.

[48] Forces under Millo's control initially consisted of the Savona Infantry Brigade, several hundred Carabinieri and customs guards, and two battalions of marines.

[50] Millo's requests for reinforcements were motivated by the possibility of a conflict with the army of the newly established Kingdom of Serbs, Croats and Slovenes, or the hostile population.

[53] Millo suppressed national liberties, and authorities in the Italian zone systematically harassed non-Italians with methods including physical assaults and confiscation of ration cards.

[17] The US presence was largely confined to the city of Split (Italian: Spalato), while the armed forces of the Kingdom of Serbs, Croats and Slovenes controlled the rest of the coast in the zone.

The provincial government consisted of Ivo Krstelj, Josip Smodlaka, and Vjekoslav Škarica; and deputies Prvislav Grisogono, Uroš Desnica, and Jerko Machiedo.

Prior to the arrival of the allied navies, public safety in Split, which was affected by shortages of food and coal, had been entrusted to 200 National Guard volunteers organised into three companies.

[58] By early 1919, the regular Army of the Kingdom of Serbs, Croats and Slovenes garrisoned the coastal settlements of Split, Trogir (Italian: Traù), and Omiš with a battalion in each, and one company was stationed in the inland town of Sinj.

In the same period, calls to the Port of Split were made by the Italian ships Carlo Mirabello, Alessandro Poerio, and Puglia, as well as US Navy's USS Israel.

Friction arose during the distribution of food and travel documents from the Italian cruiser Puglia because only the non-Italian population encountered real or perceived difficulties.

Andrews blamed both sides for the conflict, claiming the Italian force, inspired by D'Annunzio, wanted war, as did Lieutenant Colonel Milan Plesničar [sr] of the Army of the Kingdom of Serbs, Croats and Slovenes stationed in Split.

[80] The French favoured Serbian (subsequently Kingdom of Serbs, Croats and Slovenes) control of Montenegro, and facilitated the deployment of 3,000 pro-Serbian Montenegrin troops in the area.

[80] On 3 January 2019, pro-independence Greens, a faction in the Montenegrin Christmas Uprising, approached Brigadier General Paul Venel, who had replaced Caubet as the French commanding officer in the zone, requesting the allies to occupy Cetinje and deny it to the forces of Kingdom of Serbs, Croats and Slovenes.

[84] The US troops left Montenegro in early 1919,[85] while the French and the Italians limited their occupation to coastal areas of Bar and Ulcinj, the town of Virpazar on the shore of Lake Skadar, and Kotor at the southernmost tip of Dalmatia at the time, on the orders of d'Espèrey in April 1919.

[91] Military rule persisted in the Italian zone until the end of December 1920, when a special civilian commissioner was appointed in Zadar, the seat of the Province of Zara, in the aftermath of the treaty.

[87] The Treaty of Rapallo, along with the death of Nicholas I of Montenegro a few months later, marked the end of Italian support for Montenegrin resistance against the Kingdom of Serbs, Croats and Slovenes.