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 United States, Australia and Argentina. The kingdom was heavily agricultural, like the other Italian states; the church owned 50–65% of the land by 1750.
The name "Two Sicilies" originated from the partition of the medieval Kingdom of Sicily. Until 1285, the island of Sicily and the Mezzogiorno were constituent parts of the Kingdom of Sicily. As a result of the War of the Sicilian Vespers (1282–1302), the King of Sicily lost the Island of Sicily (also called Trinacria) to the Crown of Aragon, but remained ruler over the peninsular part of the realm. Although his territory became known unofficially as the Kingdom of Naples, he and his successors never gave up the title "King of Sicily" and still officially referred to their realm as the "Kingdom of Sicily". At the same time, the Aragonese rulers of the Island of Sicily also called their realm the "Kingdom of Sicily". Thus, there were two kingdoms called "Sicily": hence, the Two Sicilies.
The Kingdom of the Two Sicilies resulted from the re-unification of the Kingdom of Sicily with the Kingdom of Naples (called the Kingdom of Peninsular Sicily), by King Alfonso V of Aragon in 1442. The two states had functioned as separate realms since the War of the Sicilian Vespers in 1282. At the death of King Alfonso in 1458, the kingdom again became divided between his brother John II of Aragon, who kept the island of Sicily, and his illegitimate son Ferdinand, who became King of Naples.
In 1501, King Ferdinand II of Aragon, son of John II, conquered Naples and reunified the two kingdoms under the authority of the newly united Spanish throne. The Kings of Spain then bore the title King of Both Sicilies or King of Sicily and of the Two Coasts of the Strait until the War of the Spanish Succession. At the end of that war, the Treaty of Utrecht in 1713 granted Sicily to the Duke of Savoy until the Treaty of Rastatt in 1714 left Naples to the Emperor Charles VI. In 1720 the Emperor and Savoy exchanged Sicily for Sardinia, thus reuniting Naples and Sicily.
In 1734, Charles, Duke of Parma, son of Philip V of Spain, took the Sicilian crown from the Austrians and became Charles VII & V, giving Parma to his younger brother, Philip. In 1759, Charles became King Carlos III of Spain and resigned Sicily and Naples to his younger son, who became Ferdinand III of Sicily and Ferdinand IV of Naples, later crowned Ferdinand I of the Two Sicilies in 1816. Apart from an interruption under Napoleon, the Kingdom of the Two Sicilies remained under the Bourbon line (Bourbon Duo-Sicilie) continually until 1860.
In January 1799, Napoleon Bonaparte, in the name of the French Republic, captured Naples and proclaimed the Parthenopaean Republic, a French client state, as successor to the kingdom. King Ferdinand fled from Naples to Sicily until June of that year. In 1806, Napoleon, by then French Emperor, again dethroned King Ferdinand and appointed his brother, Joseph Bonaparte, as King of Naples. In the Edict of Bayonne of 1808 Napoleon moved Joseph to Spain and appointed their brother-in-law, Joachim Murat, as King of the Two Sicilies, though this only meant control of the mainland portion of the kingdom. Throughout this Napoleonic interruption, King Ferdinand remained in Sicily, with Palermo as his capital.