Excerpts from Books and Wikipedia
"Meanwhile, the religion of each state was to be decided by its ruler . . . (to whom the kingdom, to him the religion). Any subject who rejected his ruler's choice could migrate elsewhere. The peace applied to Catholics and Lutherans but Calvinists, Zwinglians, Anabaptists, and Mennonites were not mentioned. The agreement kept the Holy Roman Empire free of civil war for more than fifty years." [Furtado: 1001 Days] Charles V’s other great area of difficulty lay in Germany, which had been torn asunder by the Reformation and where Luther’s challenge to the old order was now being supported by a league of Protestant princely states. In view of his other problems, it was scarcely surprising that Charles V could not concentrate his energies upon the Lutheran challenge in Germany until after the mid-1540s. When he did so, he was at first quite successful, especially by defeating the armies of the leading Protestant princes at the battle of Mühlberg (1547). But any enhancement of Habsburg and imperial authority always alarmed Charles V’s rivals, so that the northern German princes, the Turks, Henry II of France (1547–1559), and even the papacy all strove to weaken his position." [Kennedy: Great Powers, p. 37]