While the emperor was thus absent great disturbances took place in Germany. Among Luther's friends was one, Ulrich von Hutten, at once penetrated with the spirit of the Renaissance and emphatically a man of action. The class to which Hutten and his friend, Franz von Sickingen, a daring and ambitious Rhenish baron, belonged, was that of the small feudal tenants in chief, the _Ritterschaft_ or knights of the Empire. This class was subject only to the emperor, but its members lacked the territorial possessions which gave power to the princes; they were partly deprived of their employment owing to the suppression of private wars, and they had suffered through the substitution of Roman law for the ancient feudal laws and customs. They had no place in the constitution or in the government of Germany, and they had already paralysed the administration by refusing to pay the taxes. They were intensely jealous of the princes, and it occurred to Hutten and Sickingen that the Reformation might be used to improve the condition of the knights and to effect a total change in the constitution of the Empire. No general reform, they maintained, either in church or state, could be secured while the country was divided into a number of principalities, and their plan was to combine with all those who were discontented with the existing order to attack the princes and to place the emperor at the head of a united nation. Sickingen, who has been compared to Wallenstein, and who doubtless hoped to secure a great position for himself, had already collected a large army, which by its very presence had contributed somewhat to the election of Charles at Frankfort in 1519. He had also earned renown by carrying on feuds with the citizens of Worms and of Metz, and now, with a view to realizing his larger ambitions, he opened the campaign (August 1522) by attacking the elector of Trier, who, as a spiritual prince, would not, it was hoped, receive any help from the religious reformers. For a moment it seemed as if Hutten's dream would be realized, but it was soon evident that it was too late to make so great a change. Luther and other persons of influence stood aloof from the movement; on the other hand, several princes, including Philip, landgrave of Hesse, united their forces against the knights, and in May 1523 Sickingen was defeated and slain. A few weeks later Hutten died on an island in the lake of Zürich. The causes of the Peasants' War.