Peace of Passau
In August 1552, weary from three decades of religious civil war, Charles guaranteed Lutheran religious freedoms in the Peace of Passau. The implementation of the Augsburg Interim was cancelled. The Protestant princes taken prisoner during the Schmalkaldic War, John Frederick of Saxony and Philip of Hesse, were released. A precursor to the Peace of Augsburg of September 1555, the Peace of Passau effectively surrendered Charles V's lifelong quest for European religious unity.