Which crusade was launched by Pope Martin IV against the Kingdom of Aragon in 1284?

The crusade launched by Pope Martin IV against the Kingdom of Aragon in 1284 was the Aragonese Crusade. It was also known as the Crusade of Aragon or the Crusade against Catalonia, and it formed part of the wider War of the Sicilian Vespers.

The conflict followed Peter III of Aragon's intervention in Sicily after the Sicilian Vespers uprising of 1282. Peter had become king of Sicily, threatening the interests of the papacy and the French-backed Angevin dynasty. Martin IV excommunicated Peter, declared Aragon forfeited and granted the crown to Charles of Valois, son of King Philip III of France.

French forces invaded Catalonia in 1285, supported by the Kingdom of Majorca, Navarre and Genoa. Although the invading army achieved some early successes, the Aragonese fleet under Roger de Lauria won control of the sea and disrupted French supplies. Disease and exhaustion weakened the crusader army during its retreat. The campaign ended in defeat for France and demonstrated that papal authorization did not guarantee military success.