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.
Sardinian medieval kingdoms
In 807, 810-812, and 821-822 the Arabs of Spain and North Africa tried to invade the island but the Sardinians resisted several attacks. This defence was so effective that in a letter in 851, Pope Leo IV asked the "Iudex Provinciae" (judge of the province) of Sardinia, based in Caralis, for aid in the defense of Rome. With the fall of the Exarchate of Africa, based in Carthage, in the eighth century, and especially with the emergence of the Arab presence in Sicily (827), Sardinia remained disconnected from Byzantium and had, out of necessity, become economically and militarily independent.