When did Sicily join Italy?
Kingdom of the Two Sicilies
The Kingdom of the Two Sicilies lasted from 1815 until 1860, when it was annexed by the Kingdom of Sardinia to form the Kingdom of Italy in 1861. The capitals of the Two Sicilies were in Naples and in Palermo. The kingdom extended over the Mezzogiorno (the southern part of mainland Italy) and the island of Sicily. Jordan Lancaster notes that the integration of the Kingdom of the Two Sicilies into the Kingdom of Italy changed the status of Naples forever: "Abject poverty meant that, throughout Naples and Southern Italy, thousands decided to leave in search of a better future." Many went to the new world. The kingdom was heavily agricultural, like the other Italian states; the church owned 50–65% of the land by 1750.
Norman conquest of southern Italy
Although the conquest of Sicily was primarily military, Robert and Roger also signed treaties with the Muslims to obtain land. Hindered by Sicily's hilly terrain and a relatively small army, the brothers sought influential, worn-down Muslim leaders to sign the treaties (offering peace and protection for land and titles). Because Sicily was conquered by a unified command, Roger's authority was not challenged by other conquerors and he maintained power over his Greek, Arab, Lombard and Norman subjects. Latin Christianity was introduced to the island, and its ecclesiastical organisation was overseen by Roger with papal approval. Sees were established at Palermo (with metropolitan authority), Syracuse and Agrigento. After its elevation to a Kingdom of Sicily in 1130, Sicily became the centre of Norman power with Palermo as capital. The Kingdom was created on Christmas Day, 1130, by Roger II of Sicily, with the agreement of Pope Innocent II, who united the lands Roger had inherited from his father Roger I of Sicily.
These areas included the Maltese Archipelago, which was conquered from the Arabs of the Emirates of Sicily; the Duchy of Apulia and the County of Sicily, which had belonged to his cousin William II, Duke of Apulia, until William's death in 1127; and the other Norman vassals.