In 1542, when Charles V. was again involved in war with France and Turkey, who were helped by Sweden, Denmark and Scotland, the league of Schmalkalden took advantage of his occupations to drive its stubborn foe, Henry, duke of Brunswick-Wolfenbüttel, from his duchy and to enthrone Protestantism completely therein. But this was not the only victory gained by the Protestants about this time. The citizens of Regensburg accepted their doctrines, which also made considerable progress in the Palatinate and in Austria, while the archbishop of Cologne, Hermann von Wied, and William, duke of Gelderland, Cleves and Juliers, announced their secession from the Roman religion. The Protestants were now at the height of their power, but their ascendancy was about to be destroyed, and that rather by the folly and imprudence of their leaders than by the skill and valour of their foes. The unity and the power of the league of Schmalkalden were being undermined by two important events, the bigamy of Philip of Hesse, which for political reasons was condoned by the Lutheran divines, and the dissensions between John Frederick, the ruler of electoral, and Maurice, the new ruler of ducal Saxony. To save himself from the consequences of his double marriage, which had provided him with powerful enemies, Philip in June 1541 came to terms with the emperor, who thus managed to spike the guns of the league of Schmalkalden, although the strength of this confederation did not fail until after the campaign against Henry of Brunswick. But while on the whole the fortunes of the European war, both in the east and in the west, were unfavourable to the imperialists, Charles V. found time in 1543 to lead a powerful force against William of Gelderland, who had joined the circle of his foreign foes. William was completely crushed; Gelderland was added to the hereditary lands of the Habsburgs, while the league of Schmalkalden impotently watched the proceedings. This happened about a year after war between the two branches of the Saxon house had only been averted by the mediation of Luther and of Philip of Hesse. The emperor, however, was unable, or unwilling, to make a more general attack on the Protestants. In accordance with the promises made to them at Frankfort in 1539, conferences between the leaders of the two religious parties were held at Hagenau, at Worms and at Regensburg, but they were practically futile. The diets at Regensburg and at Nuremberg gave very little aid for the wars, and did nothing to solve the religious difficulties which were growing more acute with repeated delays. At the diet of Spires in 1544 Charles purchased military assistance from the Protestants by making lavish promises to them. With a new army he marched against the French, but suddenly in September 1544 he concluded the treaty of Crépy with Francis I. and left himself free to begin a new chapter in the history of Germany.