The Thirty Years' War (German: Dreißigjähriger Krieg, pronounced [ˈdʁaɪ̯sɪçˌjɛːʁɪɡɐ kʁiːk] (listen)) was a conflict fought primarily in modern Germany and Central Europe. Estimates of total military and civilian deaths range from 4.5 to 8 million, mostly from disease or starvation, while it has been suggested that up to 60% of the population died in some areas of Germany. Related conflicts include the Eighty Years War, the War of the Mantuan Succession, the Franco-Spanish War, and the Portuguese Restoration War.
It was primarily seen as a German civil and religious war until 1938, when historian C. V. Wedgwood argued religion was a subsidiary factor. She suggested it originated in the long-running contest between Austro-Spanish Habsburgs and French Bourbons, a view generally accepted with certain reservations. The war can be split into two parts, the first beginning with the 1618 Bohemian Revolt and ending with the 1635 Peace of Prague. This phase was primarily a struggle for control between Emperor Ferdinand II and his German opponents, with external powers playing a lesser role. In the second, Germany became part of a wider European struggle, with Sweden and France on one side, the Spanish and Austrian Habsburgs on the other, concluded with the 1648 Peace of Westphalia.
Conflict between German Protestants and Catholics caused by the early 16th century Reformation had been temporarily settled by the 1555 Peace of Augsburg. This agreement was gradually undermined by political and religious tensions, and in 1618 the Protestant-dominated Bohemian Estates deposed the Catholic Ferdinand II as King of Bohemia. They offered the Crown to the Protestant Frederick V of the Palatinate, but most German princes refused to support him, and by early 1620 the Bohemian Revolt had been suppressed. This was the first of many points at which the conflict could have ended but did not.
When Frederick refused to admit defeat, the war expanded into the Palatinate, whose strategic importance drew in external powers, notably the Dutch Republic and Spain. By 1623, Spanish-Imperial forces defeated Frederick, who was stripped of his possessions and exiled. Combined with his support for the Catholic Counter-Reformation, this threatened other Protestant rulers within the Empire, including Christian IV of Denmark, who was also Duke of Holstein; in 1625 he intervened in Northern Germany until forced to withdraw in 1629.
Ferdinand now passed the Edict of Restitution, which sought to restore Catholic property lost at Augsburg and effectively destabilised large areas of North and Central Germany. Doing so provided an opportunity for Gustavus Adolphus of Sweden, who invaded the Empire in 1630, backed by French subsidies. Over the next four years, the Swedes and their German allies won a series of victories over Imperial forces, although Gustavus was killed in 1632. At Prague in 1635, Ferdinand accepted the autonomy of the German states and in return they dissolved the Heilbronn and Catholic Leagues.
The defection of their German allies led France to enter the conflict directly as part of their struggle with Spain. Although their war continued until 1659, fighting in Germany ended with the 1648 Peace, whose main provisions included acceptance of "German liberties" by the Emperor and Dutch independence by Spain. By weakening the Habsburgs relative to France and its allies, it altered the European balance of power and set the stage for the wars of Louis XIV.