Charles' only ally in North Germany, and occupied his territories. The patriotism of the Netherlands held the French in check. Charles returned from Spain and, in 1543, attacked Cleves. A few days sufficed to make Guelders a part of Burgundy, which was thus protected on the side of Germany, though still exposed on its French frontier. It was to remedy this weakness that Charles established a line of fortresses which for centuries barred the way against French invasion. In 1544 he invaded France. The strength of Francis was exhausted, and, as Charles, too, was weary of war, a peace was concluded at Crespy (17 September, 1544). Charles had now to consider whether he would allow liberty of action to the Protestant princes of Germany, to whom, under pressure of war, he had made concessions, especially at the Diet of Spires in 1544. Up to this time he had let affairs take their own course in Germany, and his brother Ferdinand bad been unable to exert effectual pressure. The power of the feudatory princes, steadily increasing since 1521, was now established on a solid basis. In the emperor's absence they had, on their own initiative, found means to suppress several disturbances which might otherwise have plunged Germany into the horrors of civil warfirst the League of the Knights, then the Peasants' War, then the disorders of the turbulent clergy who had embraced Lutheranism and led the masses astray, and lastly the rebellion of the Anabaptists (q. v.). By supporting Luther against Charles, the princes secured the means of maintaining the power which they had acquired by their resistance to the emperor. Charles perceived the gravity of the situation at least sufficiently to lead him to resolve upon open war against the princes. To deprive them of their religious leverage, he awaited the opening of the Council of Trent (1545). In the summer of 1546 he opened hostilities. He began by conquering South Germany, then pushed forward into Saxony, an...
