The Thirty Years’ War was the bloodiest religious conflict in Europe, costing around 8 million lives. It lasted from 1618 to 1648, and originated in religious rivalries between the protestants and the Catholics, but morphed into a more political conflict between France and the Holy Roman Empire.
Ferdinand II of Bohemia (1578-1637), a devout Catholic, took actions against the protestants in revoking some of their privileges. These actions lead to the Defenestration of Prague in 1618 in which two royal officials and a secretary were thrown out of a window by Protestants. Ferdinand did not adopt a policy of religious toleration, and was declared deposed as king of Bohemia in the Bohemian Revolt (1618-1620). A protestant, Frederick V, was then declared king. This worried the Catholic Hapsburgs because the office of Holy Roman Emperor was elected by several offices called electorates. The office of king of Bohemia was an electorate, and Frederick V was already an elector, so he would now have two votes for the election of the next Holy Roman Emperor. There were only seven votes, and two of them were already protestant. That means that there would be a four-to-three protestant majority. In addition to this new balance of power, Frederick launched an anti-Catholic campaign, destroying altars and sacred images. Ferdinand responded by bringing in the Imperial army. In the ensuing conflict, the protestant forces suffered several defeats.
The war following the Bohemian revolt was divided into into several stages. The firs was the Danish stage, lasting from 1624 to 1629, in which king Christian IV of Denmark entered the conflict. Ferdinand II asked for the help of Albrecht Von Wallenstein, a military leader and nobleman. With Wallenstein Frederick had successes, and was persuaded that he could carry out the edict of restitution, which would bring back Catholic lands. He dismissed Wallenstein, but Wallenstien knew that he would be needed again for the Swedish threat. Next was the Swedish phase, which lasted from 1630 to 1635. The protestant Swedish king, Gustavus Adolphus, allied with Catholic France against the Holy Roman Empire. Just as Wallenstien predicted, he was recalled by Ferdinand to deal with Gustavus. Gustavus was killed at the battle of Lützen in 1632, even though the Swedish forces prevailed. Wallenstein was killed on official orders by Ferdinand after it appeared that he was seeking power for himself. The last stage was the Franco-Hapsburg phase, in which the war shifted to a more direct conflict between France and the Holy Roman Empire.
The war ended with the Peace of Westphalia in 1648, which was ultimately a protestant victory. The protestants were allowed freedom of worship in public at special times, and freedom in private all the time. The Important long-term consequence of the Thirty Years’ war was that religion now fell into the background in European affairs. There was no longer a Christendom to which everybody belonged, and there was no longer the universal authority of the Catholic Church (and of the Pope) that could intervene in relations between countries. Conflicts like the Thirty Years’ War and the French Wars of Religion contributed to the secularization of world affairs.