Being now at the height of his power Charles wished to secure the succession to the imperial throne to his son Philip, afterwards Philip II. of Spain. This intention produced dissensions among the Habsburgs, especially between the emperor and his brother Ferdinand, and other causes were at work, moreover, to undermine the former's position. The Romanist princes were becoming alarmed at his predominance, the Protestant princes resented his arbitrary measures and disliked the harsh treatment meted out to John Frederick and to Philip of Hesse; all alike, irritated by the presence of Spanish soldiers in their midst, objected strongly to take Philip for their king and to any extension of Spanish influence in Germany. Turkey and France were again threatening war, and although the council had returned to Trent it seemed less likely than ever to satisfy the Protestants. The general discontent found expression in the person of Maurice of Saxony, a son-in-law of Philip of Hesse, whose services to Charles against the league of Schmalkalden had made him very unpopular in his own country. Caring little or nothing about doctrinal disputes, but a great deal about increasing his own importance, Maurice now took the lead in plotting against the emperor. He entered into an alliance with John, margrave of Brandenburg-Cüstrin, with another Hohenzollern prince, Albert Alcibiades of Bayreuth, and with other Lutheran leaders, and also with Henry II. of France, who eagerly seized this opportunity of profiting by the dissensions in the Empire and who stipulated for a definite reward. Charles knew something of these proceedings, but his recent victory had thrown him partly off his guard. The treaty with France was signed in January 1552; in March Henry II. invaded Germany as the protector of her liberties, while Maurice seized Augsburg and marched towards Innsbruck, where the emperor was residing, with the intention of making him a prisoner. An attempt at accommodation failed; Charles fled into Carinthia; and at one stroke all the advantages which he had gained by his triumph at Mühlberg were lost. Masters of the situation, Maurice and his associates met their opponents at Passau in May 1552 and arranged terms of peace, although the emperor did not assent to them until July. The two captive princes were released, but the main point agreed upon was that a diet should be called for the purpose of settling the religious difficulty, and that in the meantime the Lutherans were to enjoy full religious liberty. The peace of Augsburg.