He was the son of Philip, Duke of Burgundy, by Joanna, daughter of Ferdinand and Isabella. He succeeded his father in 1506 as Charles I, King of Spain, and was declared the successor of Ferdinand of Aragon in 1516. In 1520 he was elected Holy Roman Emperor in the face of the opposition of Rome and France. At the Diet of Worms in 1521, he appealed in person against Luther. In 1522 he gave his Austrian possessions to his brother Ferdinand and established a permanent regency for the Netherlands. From 1521 to 1529 he waged war against Francis I, whom he defeated at Pavia, Italy in 1525, and after the French coalition with Pope Clement VII, marched against Rome, which was sacked by undisciplined troops in 1521. The Peace of Cambrai (1529) concluded the struggle. Charles established legislation which regulated the social and industrial life of the Netherlands, adopted a progressive policy in Spain, and dealt successfully with colonial politics in America. He received the imperial crown from Clement VII, at Bologna on 24 February 1530. In a campaign against the Turks he conquered Tunis, in 1535. A renewal of hostilities with Francis I resulted in the Peace at Crespy (1544). The general council, which he had urged, was convoked at Trent (1545). Soon after he began hostilities against the Smalkaldic League, and following the defeat of the Protestant princes he sought to enlist their services in the reorganization of the Empire. In 1552, however, they attacked his forces and by the Treaty of Passau gained ascendancy in the Empire. Having transferred the government of the Netherlands and the Spanish Crown to his son Philip, in 1556 he abdicated the imperial throne in favor of his brother Ferdinand and retired to the monastery of Yuste. Here he was informed of political affairs, but ceased to take an active part in them.