During the 1530s and early 1540s Charles was mostly preoccupied with the Ottoman threat. In 1545, however, he turned his attention to the Schmalkaldic League. In 1547 his troops soundly defeated a Saxon army at Mühlberg, and the emperor’s ascendancy was assured. In 1548, at the peak of his power, Charles issued the Augsburg Interim, an attempt to end religious division within the empire by some minor concessions to Lutherans. This interim settlement failed to appease Protestant princes and threatened to provoke a much more destructive civil war within the empire. A compromise was reached in the Peace of Augsburg, which Charles reluctantly accepted in 1555. This treaty became the foundation for religious coexistence in Germany for the next three centuries. Most importantly, it granted the princes and cities full sovereignty regarding religion.

Each ruler could choose either Lutheranism or Catholicism as the official religion of his territory (the Reformed and Calvinist creeds, while not prohibited, were not recognized by the Peace of Augsburg). He was free to treat nonconformist subjects as he wanted, sometimes forcing them to migrate or convert. Religious segregation, rather than toleration, seemed the only solution, and for the rest of the century at least, it seemed to work. Encarta