The excommunication of King Peter III of Aragon by Pope Martin IV stemmed from Peter's aggressive actions in Sicily. Following the revolt known as the Sicilian Vespers in 1282, Peter took control of the island which rightfully belonged to the French Angevins. The Pope viewed Peter's ascendancy not only as a political maneuver but also as a direct challenge to papal supremacy in matters of sovereignty. Pope Martin IV, having been an ally of the French Angiovins, sought to assert his authority and maintain the political balance in the region. This excommunication was not an isolated decree; it was reaffirmed on two occasions, reflecting the ongoing tensions between the kingdoms in Italy and the influence of the Roman Catholic Church over European monarchies.

The context of this conflict is rooted in the broader geopolitical struggles of the time. The Islanders had revolted against King Charles of Anjou—an ally of the Pope—leading to a severe crisis as rival powers vied for control over Sicily. The renewal of excommunications highlighted the Pope’s desperation to regain influence and curb the Aragonese ambitions. It illustrated the complex interplay between Papal authority and the monarchy, revealing how intertwined religion and politics were during this period. As a result, the excommunication also served to galvanize support for Charles’s cause among other European leaders who were loyal to the papacy and sought to restore the Angevin crown to Sicily.