Gustavus Adolphus, having strengthened himself by a formal agreement with France, marched into Germany at the head of a body of picked troops (1630). He issued a proclamation announcing that he had come to free the Germans from slavery, and he opened negotiations with the Protestant princes, some of whom to do them justice showed themselves very reluctant to become allies of a foreign invader. Ferdinand II. was but poorly prepared to meet such an attack. The imperial troops had been disbanded, and what was much worse, Wallenstein had retired into private life. Many of the Catholic princes, notably Maximilian of Bavaria, resented his rapid promotion and the grant that had been made to him of the Duchy of Mecklenburg. They prejudiced the mind of Ferdinand against him just at the time his services were most urgently required. Nor, when the first fit of zeal had passed away, were all the Catholic princes anxious to hasten to the support of the Emperor. Tilly with the forces of the /League/ advanced to bar the progress of the Swedes. He was defeated at Breitenfeld (1631) and his army was nearly destroyed. Gustavus Adolphus pushed rapidly forward towards Bavaria, captured the cities of Wurzburg, Mainz, and Augsburg, and for a time it seemed as if his advance to Vienna was going to be a triumphal march. Over-joyed with the success of his campaign he began to act as if he were really emperor of Germany, thereby giving great offence to many of his German followers. His dreams of power were, however, brought to an abrupt termination. In April 1632 he fought an indecisive battle at Rain on the Lech, where Tilly was wounded mortally, but in November he was slain at Lutzen though his army was victorious.