Origins of the war[edit]
The Peace of Augsburg (1555), signed by Charles V, Holy Roman Emperor, confirmed the result of the 1526 Diet of Speyer, ending the war between German Lutherans and Catholics, and establishing that:[16]
Rulers of the 224 German states could choose the religion (Lutheranism or Catholicism) of their realms according to their consciences, and compel their subjects to follow that faith (the principle of cuius regio, eius religio).
Lutherans living in a prince-bishopric (a state ruled by a Catholic bishop) could continue to practice their faith.
Lutherans could keep the territory they had taken from the Catholic Church since the Peace of Passau in 1552.
Those prince-bishops who had converted to Lutheranism were required to give up their territories (the principle called reservatum ecclesiasticum).
Although the Peace of Augsburg created a temporary end to hostilities, it did not resolve the underlying religious conflict, which was made yet more complex by the spread of Calvinism throughout Germany in the years that followed.[17] This added a third major faith to the region, but its position was not recognized in any way by the Augsburg terms, to which only Catholicism and Lutheranism were parties.[18][19]
The rulers of the nations neighboring the Holy Roman Empire also contributed to the outbreak of the Thirty Years' War:
Spain was interested in the German states because it held the territories of the Spanish Netherlands in the western part of the Empire and states within Italy that were connected by land through the Spanish Road. The Dutch revolted against Spanish domination during the 1560s, leading to a protracted war of independence that led to a truce only in 1609.
France was nearly surrounded by territory controlled by the two Habsburg states – Spain and the Holy Roman Empire, and feeling threatened, was eager to exert its power against the weaker German states. This dynastic concern overtook religious ones and led to Catholic France's participation on the otherwise Protestant side of the war.
Sweden and Denmark were interested in gaining control over northern German states bordering the Baltic Sea.