For a long time following Ferdinand III's creation in 1296 of an independent Kingdom of Sicily separate from the mainland territory surrounding Naples, the crown of Sicily descended in a Spanish line while the crown of Naples descended through the hands of their ancient enemies, the descendants of Charles II of Anjou.

A remarkable Renaissance individual, Alphonso V, King of Aragon--called "the Magnanimous"--finally united the old enemies. Alphonso first gained the throne of Sicily by inheritance. Later, Queen Joanna II of Naples--whose four husbands and myriad lovers would scarcely seem to have left her time for governance--solicited Alphonso's aid in fending off a variety of claimants to her throne. As recompense she promised to make Alphonso her heir to the crown of Naples. Alphonso launched a military campaign that by 1422 restored Joanna to Naples. Joanna was a fickle ally, however, and she soon found a new favorite whom she preferred to be her heir. Following Joanna's death in 1435 Alphonso returned to enforce his claim by force of arms. In 1443 Pope Eugene IV acknowledged Alphonso's conquest of Naples and his seat upon its throne.

Alphonso was a man of letters himself and an early leader of the renaissance in classical studies. He carried the works of classical writers with him on his military campaigns and once halted his army in mid-march to honor the birthplace of a Latin writer.

Following Alphonso's death, the reunited territory of Sicily and Naples descended through successive generations as a possession of the Spanish monarch.