History of Sardinia
In the Early Middle Ages, through barbarian movements, the waning of the Byzantine Empire influence in the western Mediterranean and the Saracen raids, the island fell out of the sphere of influence of any higher government. This led to the birth of four kingdoms called "Judicates" (Latin: "Judicati"; Sardinian: "Judicados") in the 8th through 10th centuries. Falling under papal influence, Sardinia became the focus of the rivalry of Genoa and Pisa, the Judicates and the Crown of Aragon, which eventually subsumed the island as the Kingdom of Sardinia in 1324. The Kingdom was to last until 1718, when it was ceded to the Piedmontese House of Savoy; later, in 1861, it would thus become the Kingdom of Italy and finally in 1946 the Italian Republic.
Sardinia
In 1297, Pope Boniface VIII established on his own initiative ("motu proprio") a hypothetical "regnum Sardiniae et Corsicae" ("Kingdom of Sardinia and Corsica") in order to settle the War of the Sicilian Vespers diplomatically. This had broken out in 1282 between the Capetian House of Anjou and Catalans over the possession of Sicily. Despite the existence of the indigenous states, the Pope offered this newly created crown to James II of Aragon, promising him support should he wish to conquer Pisan Sardinia in exchange for Sicily.
In 1324, in alliance with the Kingdom of Arborea and following a military campaign that lasted a year or so, the Aragon Crown Prince Alfonso led a Catalan army that occupied the Pisan territories of Cagliari and Gallura along with the allied city of Sassari, naming them ""The Kingdom of Sardinia and Corsica"". The kingdom was to remain a dominion of the Crown of Aragon (under the Kings of Spain) until the Treaty of Utrecht.