page_title: Thirty Years' War
section_title: Origins of the war
hierarchical_section_title: Thirty Years' War / Origins of the war
context_page_description: The Thirty Years' War was a religious and geopolitical war fought primarily in Central Europe between 1618 and 1648. It resulted in the deaths of over 8 million people, including 20% of the German population, making it one of the most destructive conflicts in human history. Initially a war between the Protestant and Catholic states in the Holy Roman Empire, it gradually developed into a general European war, involving most of the great powers. The war, and the smaller wars it produced, became less about religion and more of a continuation of the French–Habsburg rivalry for European political pre-eminence, and a Habsburg attempt to rebuild imperial authority in Germany.
  The war was instigated by the election of Ferdinand II as Holy Roman Emperor, a staunch Catholic who tried to impose religious uniformity on his domains. In response, the Protestant states of northern Germany formed the Protestant Union to defend their interests. Tensions grew until the Defenestration of Prague, when Bohemian Protestants threw the Emperor's representatives out of a window. The Bohemians then elected the Protestant Frederick V, Elector Palatine, as the new king of the Kingdom of Bohemia.
context_section_description: The Peace of Augsburg (1555), signed by Charles V, Holy Roman Emperor, confirmed the result of the Diet of Speyer (1526), ending the war between German Lutherans and Catholics, and establishing that:
  Rulers of the 224 German states could choose the religion (Lutheranism or Catholicism) of their realms. Subjects had to follow that decision or emigrate (the principle of cuius regio, eius religio).
  Prince-bishoprics and other states ruled by Catholic clergy were excluded and should remain Catholic. Prince-bishops who converted to Lutheranism were required to give up their territories (the principle called reservatum ecclesiasticum).
  Lutherans could keep the territory they had taken from the Catholic Church since the Peace of Passau in 1552.
  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. 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.
  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-Norway were interested in gaining control over northern German states bordering the Baltic Sea.
  The Holy Roman Empire was a fragmented collection of largely independent states (a fragmentation that the Peace of Westphalia would solidify). The position of the Holy Roman Emperor was mainly titular, but the emperors, from the House of Habsburg, also directly ruled a large portion of imperial territory (lands of the Archduchy of Austria and the Kingdom of Bohemia), as well as the Kingdom of Hungary. The Austrian domain was thus a major European power in its own right, ruling over some eight million subjects. Another branch of the House of Habsburg ruled over Spain and its empire, which included the Spanish Netherlands, southern Italy, the Philippines, and most of the Americas. In addition to Habsburg lands, the Holy Roman Empire contained several regional powers, such as the Duchy of Bavaria, the Electorate of Saxony, the Margraviate of Brandenburg, the Electorate of the Palatinate and the Landgraviate of Hesse. A vast number of minor independent duchies, free cities, abbeys, prince-bishoprics, and petty lordships (whose authority sometimes extended to no more than a single village) rounded out the empire. Apart from Austria and perhaps Bavaria, none of those entities was capable of national-level politics; alliances between family-related states were common, due partly to the frequent practice of partible inheritance, i.e. splitting a lord's inheritance among his various sons.
  Religious tensions remained strong throughout the second half of the 16th century. The Peace of Augsburg began to unravel: some converted bishops refused to give up their bishoprics, and certain Habsburg and other Catholic rulers of the Holy Roman Empire and Spain sought to restore the power of Catholicism in the region. This was evident from the Cologne War (1583–88), a conflict initiated when the prince-archbishop of the city, Gebhard Truchsess von Waldburg, converted to Calvinism. As he was an imperial elector, this could have produced a Protestant majority in the College that elected the Holy Roman Emperor, 
caption: Ferdinand II, Holy Roman Emperor and King of Bohemia, whose staunch Catholicism and diligent opposition to Protestantism contributed to the war's outbreak.
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