Its territory of 28 km2 (11 sq mi) comprised the city of Fiume (today Rijeka, Croatia) and rural areas to its north, with a corridor to its west connecting it to the Kingdom of Italy.

Fiume gained autonomy for the first time in 1719, when it was proclaimed a free port of the Holy Roman Empire in a decree issued by the Emperor Charles VI.

The city briefly lost its autonomy in 1848 after being occupied by Croatian ban (viceroy) Josip Jelačić but regained it in 1868, when it rejoined the Kingdom of Hungary, again as a corpus separatum.

D'Annunzio refused to acknowledge the agreement and was expelled from the city by the regular forces of the Italian Army, in the "Bloody Christmas" actions from 24 to 30 December 1920.

Following the departure of D'Annunzio's troops in December 1920, the Italian National Council of Fiume reassumed control and appointed a provisional government.

In October, autonomist Riccardo Zanella was appointed provisional president; his rule lasted until 3 March 1922, when Italian Fascists carried out a coup d'état and the legal government escaped to Kraljevica.

[11] In the aftermath of the Second World War, Zanella and Tito were still discussing the possibility of reinstating the old free state, but changes in the international geopolitical picture led the Yugoslav Communist regime to seize the opportunity and annex the city in 1947 after two years of occupation, aided by Stalin's strong support during the Paris peace conference.

In 1944, a group of citizens issued the Liburnia Memorandum,[12] in which it was recommended that a confederate state be formed from the three cantons of Fiume, Sušak, and Ilirska Bistrica.

The islands of Krk (Veglia), Cres (Cherso), and Lošinj (Lussino) would enter the common condominium (a government operating under joint rule) as well.

[14] The Yugoslav authorities, who took possession of the city from German occupation on 3 May 1945, objected to the plans and took concrete steps to settle the dispute.