Between April and June 1563 the Regency of Algiers launched a major military campaign to retake the Spanish military-bases of Oran and Mers el Kébir on the North African coast, occupied by Spain since 1505. The sieges of Oran and Mers El Kébir of 1563 represented a major Hispano-Algerian episode in the larger Ottoman-Habsburg wars of the Mediterranean. The Kingdom of Algiers, the Principalities of Kabyle, and other vassal tribes combined forces as one army under Hasan Pasha, son of Hayreddin Barbarossa, and Jafar Catania. The Spanish commander brothers, Alonso de Córdoba Count of Alcaudete and Martín de Córdoba, managed to hold the strongholds of Oran and Mers El Kébir, respectively, until the relief fleet of Francisco de Mendoza arrived to successfully defeat the offensive.

The Regency of Algiers was a largely independent tributary state of the Ottoman Empire during the early modern period, located on the Barbary Coast of North Africa from 1516 to 1830. Founded by the corsair brothers Aruj and Hayreddin Barbarossa, the Regency was a formidable pirate base infamous for its corsairs. First ruled by Ottoman regents, it later became a sovereign military republic that plundered and waged maritime holy war against European Christian powers.