The ethnic Italian portion of the population of Fiume welcomed D'Annunzio enthusiastically,[2] and on the same day, he announced that he had annexed the territory to the Kingdom of Italy.

The Italian government opposed this and attempted to pressure D'Annunzio into withdrawing by initiating a blockade of Fiume and demanding that the plotters surrender.

[3] During his time in Fiume in September 1919, the Italian poet, editor, and art theorist, Filippo Tommaso Marinetti, the founder of the Futurist movement, praised the leaders of the impresa as "advance-guard deserters" (disertori in avanti).

[5] After the National Council's decision, D'Annunzio addressed a crowd of 5,000 people and incited them to reject the modus vivendi, promising to put the issue to a plebiscite.

According to historian Michael Ledeen, D'Annunzio made this decision because he distrusted the Italian government and doubted its ability to deliver on its promises.

However, D'Annunzio coauthored the charter with syndicalist Alceste De Ambris, who would emerge as a prominent Anti-Fascist and go into exile following Mussolini's seizure of power.

Joint sessions of both councils (Arengo del Carnaro) would be responsible for treaties with foreign powers, amendments to the constitution, and appointment of a dictator in times of emergency (this derived from the institutions of the ancient Roman Republic).

[8] It also included his method of government in Fiume: the economics of the corporate state; stage tricks; large emotive nationalistic public rituals; and blackshirted followers, the Arditi, with their disciplined, bestial responses and strongarm repression of dissent.

Antonio Gramsci, who distrusted D'Annunzio, considered that his movement had appreciable popular elements, and Lenin advised an alliance of the Soviet Union with Carnaro's Italian Regency.

Since D'Annunzio's legionaries were refusing to surrender and were strongly resisting the attack using machine guns and grenades, the Italian dreadnoughts Andrea Doria and Duilio opened fire on Fiume and bombarded the city for three days.

The Free State of Fiume lasted officially until 1924, when the Kingdom of Italy formally annexed it under the terms of the Treaty of Rome of 1924.