Excerpts from Books and Wikipedia
"The rebellion, which came to be known as the Revolt of the Sicilian Vespers, turned into war when the Sicilians offered Peter III, King of Aragon, the Sicilian throne. However, in response to the rebellion, Charles I landed a force at Messina and besieged the city. But Charles's army was attacked by Peter's Aragonese forces, and they soon abandoned Sicily. For the next twenty years, the War of the Sicilian Vespers continued to rage throughout the Mediterranean between the Angevin kings of France, their relatives, and the papacy on one side, and the Aragonese kings on the other. The conflict came to an end in 1302 with the Treaty of Caltabellotta, in which the Kingdom of Sicily was partitioned into the island of Sicily and southern Italy, which later came to be known as the Kingdom of Naples." [Furtado: 1001 Days] Duke Charles of Anjou had claimed the throne of Sicily in 1266. His administrators and high taxes soon alienated the populace. A rebellion began on 29 March 1282 in the city of Palermo, at about the time of evening prayer (vespers), thus giving the war its name. King Pedro of Aragon, who had a claim to Sicily, made common cause with the rebels." [Battles of the Medieval World]