Victory of Charles over the league of Schmalkalden.
Charles was now nearly ready to crush the Protestants, whose influence and teaching had divided Germany and weakened the imperial power, and were now endangering the supremacy of the Habsburgs in the Netherlands and in Alsace. His plan was to bring about the meeting of a general council to make the necessary reforms in the church, and then at whatever cost to compel the Protestants to abide by its decisions. While Pope Paul III., somewhat reluctantly, summoned the council which ultimately met at Trent, Charles made vigorous preparations for war. Having made peace with the Turks in October 1545 he began to secure allies. Assistance was promised by the pope; the emperor purchased the neutrality of Duke William of Bavaria, and at a high price the active aid of Maurice of Saxony; he managed to detach from the league of Schmalkalden those members who were without any enthusiasm for the Protestant cause and also those who were too timid to enter upon a serious struggle. Meanwhile the league was inactive. Its chiefs differed on questions of policy, one section believing that the emperor did not intend to proceed to extremities, and for some time no measures were taken to meet the coming peril. At last, in June 1546, during the meeting of the diet at Regensburg, Philip and John Frederick of Saxony realized the extent of the danger and began to muster their forces. They were still much more powerful than the emperor, but they did not work well together, or with Sebastian Schärtlin von Burtenbach, who led their troops in South Germany. In July 1546 they were placed under the imperial ban, and the war began in the valley of the Danube. Charles was aided by soldiers hurried from Italy and the Netherlands, but he did not gain any substantial successes until after October 1546, when his ally Maurice invaded electoral Saxony and forced John Frederick to march northwards to its defence. The Lutheran cities of southern and central Germany, among them Strassburg, Augsburg, Ulm and Frankfort, now submitted to the emperor, while Ulrich of Württemberg and the elector palatine of the Rhine, Frederick II., followed their example. Having restored Roman Catholicism in the archbishopric of Cologne and seen Henry of Brunswick settled in his duchy early in 1547, Charles led his men against his principal enemies, Philip of Hesse and John Frederick, who had quickly succeeded in driving Maurice from his electorate. At Mühlberg in April 1547 he overtook the army of the Saxon elector. His victory was complete. John Frederick was taken prisoner, and a little later Philip of Hesse, after vainly prolonging the struggle, was induced to surrender. The rising in the other parts of northern Germany was also put down, and the two leaders of political Lutheranism were prisoners in the emperor's hands.