King of Spain (1516-1556) and Holy Roman Emperor (1520-1556), and initiator of three major campaigns that could be considered crusades: in central Europe in 1532, against Tunis in 1535, and against Algiers in 1541.
Charles was the son of Philip the Fair (d. 1506), ruler of the Habsburg Netherlands, and of Joanna, infanta of Spain, who was the daughter of the two “Catholic Monarchs,” Ferdinand II of Aragon and Isabella I of Castile. By the time he was crowned Holy Roman Emperor at the age of nineteen, Charles had succeeded to Spain and the Habsburg lands in Austria and the Netherlands.
Charles had vowed to maintain peace with Christians and warfare against Muslims, but political realities prevented him from fulfilling his vow. His reign was marked by the Protestant Reformation, conflict with France, and rivalry with the Ottoman sultan, Süleyman the Magnificent, in central Europe and the western Mediterranean. Charles committed imperial resources against the Ottomans in central Europe to protect the interests of his younger brother (later emperor), Ferdinand (d. 1564). Ferdinand claimed the throne of Hungary after the death of King Louis II at the battle of Mohacs in 1526, but Süleyman recognized a rival candidate, John Szapolyai. The Turks unsuccessfully besieged Vienna in 1529; in 1532 Ferdinand relieved the Turkish siege of Koszeg(Güns), and in 1533 Süleyman agreed to a division of Hungary between Ferdinand and Szapolyai.
The Ottoman conquest of Egypt in 1517 shifted the balance of power in the Mediterranean. The Turks established Algiers and Tripoli as outposts, threatening Spain’s interests in the western Mediterranean. Charles expanded his naval forces, acquiring a major Mediterranean fleet when the Genoese admiral, Andrea Doria, defected to him from Francis I of France in 1528. After Süleymanexpelled the Hospitallers from Rhodes in 1522, Charles offered them the island of Malta, with additional responsibility for Tripoli. The order accepted Charles’s offer in 1530. These precautions sheltered the stretch of sea near Naples and Sicily and shielded Spain from Ottoman expansion. For his part, Süleyman acquired the services of the ruler of Algiers, Khayr al-Dīn Pasha (known in the West as Barbarossa), who seized the island fortress of Penôn of Algiers from Spain in 1529.
Charles organized an expedition against Barbarossa in Tunis in 1535 to remove Süleyman’s fleet and secure the western Mediterranean. Under the command of Charles and Doria, the expedition captured the fortress of La Goleta and the city of Tunis. Barbarossa escaped to Istanbul, where he took command of the sultan’s navy in the eastern Mediterranean. Charles’s other rival, Francis I of France, made an alliance with Süleyman against Charles in 1536. In response, in 1538 Charles formed the Holy League with Venice and the papacy to fight Barbarossa off the coast of Greece. He began planning a Mediterranean crusade against Algiers in 1541, but the Christians abandoned it when their fleet was wrecked in a storm.
Although Barbarossa died in 1546, Ottoman expansion in North Africa remained a threat to the Habsburg interests in Spain. Charles’s obligations in northern Europe prevented him from giving his full attention to the Mediterranean, and his plans to lead an armada against Istanbul were interrupted by other wars in Europe. In 1555-1556 he abdicated from rule in all his dominions and retired to a Spanish monastery.