The Catholic princes, alarmed by the rapid spread of the new doctrines and by the extravagant demands of the Protestants, met together to form the Holy League (1538) as a defence against the Schmalkaldic confederation. Feeling was running so high at the time that the long expected war might have broken out immediately, had not the dread of a Turkish invasion exercised a restraining influence on both parties. In 1539 negotiations were opened up for a temporary armistice, and another fruitless attempt was made to arrive at peace by means of a religious conference. Before any result had been attained the Emperor summoned a Diet to meet at Ratisbon (April 1541). Three theologians were appointed from both sides to discuss the questions at issue. Though some of the Catholic representatives showed clearly enough that their desire for union was much greater than their knowledge of Catholic principles, an understanding was arrived at only in regard to a few points of difference. By the Recess of the Diet (known as the /Ratisbon Interim/) it was ordered that both parties should observe the articles of faith on which they had agreed until a General Council should meet, that in the interval the terms of the Peace of Nurnberg should be carried out strictly, that the religious houses that had escaped destruction hitherto should remain undisturbed, and that the disciplinary decrees promulgated by the cardinal legate (Contarini) should be obeyed by the Catholics. The Protestant princes were still dissatisfied. In order to procure their assistance Charles was obliged to yield to further demands, notably, to permit them to suppress the monasteries in their dominions. But, fortunately for the Catholic Church, the agreement embodied in the /Ratisbon Interim/ was rejected by the more extreme Protestant Party led by Luther himself, and the danger of grave misunderstanding was removed. During the following years the Lutheran movement continued to advance by leaps and bounds. Duke George of Saxony, one of its strongest opponents, died in 1539, and his successor invited the Lutheran preachers to assist him in the work of reform. Henry, Duke of Brunswick, was driven from his kingdom by the League of Schmalkald and forced to seek refuge in Bavaria. The Bishoprics of Hildesheim and Naumburg were captured by force, and it required all the efforts of the Pope and of the Emperor to prevent Cologne from being handed over to Luther's followers by its prince-bishop (Hermann von Wied). Lutheranism provided almost irresistible attractions for the lay rulers, who desired to acquire wealth and power at the expense of the Church, as well as for the unworthy ecclesiastical princes who were anxious to convert the states of which they were merely administrators into hereditary dominions.