This series of four related wars, known collectively as the Thirty Years' War, began as religious conflict but soon became a cauldron of political ambition. After bringing great devastation to Germany, the war ended with the Peace of Westphalia in 1648, a date commonly used to mark the end of the Era of Reform. The Peace of Westphalia defined the religious boundaries of Europe for some time to come. It recognized some regions as firmly Protestant, while Austria and Bohemia remained firmly Catholic. Under the treaty, German Calvinists secured the legal right to exist but radical Protestants did not. The overall principle was "territorialism." In this strategy for dealing with rival religious claims, secular rulers determined the religion to be followed within their domains as expressed in the slogan cuius regio eius religio: "whose the realm, his is the religion." Exceptions were made for territories that had more than one religious party before 1624, provided those groups did not expand. The suffering inflicted by the war convinced many people that armies could not solve religious differences. A new strategy, toleration, was soon articulated by John Locke.