The Thirty Years' War was a war fought primarily in Central Europe between 1618 and 1648. It resulted in the deaths of over 8 million people, including 20 percent 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 became less about religion and more of a continuation of the France–Habsburg rivalry for European political pre-eminence and a Habsburg attempt to rebuild the 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 (1618), 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. The Catholic states of southern Germany, led by Bavaria, formed the Catholic League to help the Emperor restore his authority in Bohemia. The Bohemian Revolt was crushed in the Battle of White Mountain (1620), and the Protestant Union dissolved in 1621. Protestant resistance was crushed at the Battle of Stadtlohn (1623), ending the Palatine phase of the Thirty Years' War.
The decisive Catholic victory would not last, as other Protestant countries entered the war to defend their brethren in Germany. Protestant Denmark intervened unsuccessfully in 1625–1630. The Protestant cause was then taken up by Gustavus Adolphus, King of Sweden, with the financial support of France. Although the Bourbon Kings of France were Catholic, their main rivals for European leadership were the Habsburg rulers of the Holy Roman Empire and Spain. Initial Swedish successes brought them deep into Catholic territory in southern Germany, but Swedish fortunes ebbed after Gustavus Adolphus was killed at the Battle of Lützen (1632). France then entered the war directly on the Protestant side in 1635. What had begun as a rebellion against Habsburg authority in Bohemia had expanded into a general European war.
The Thirty Years' War devastated entire regions, resulting in high mortality from hunger and disease. Campaigning armies and mercenaries funded themselves by looting or by exacting contributions from the inhabitants of occupied territories, imposing severe hardships on the populace. The war also bankrupted most of the combatant powers. Finally, the exhausted combatants negotiated the Peace of Westphalia (1648), putting an end to the overlapping conflicts. The rise of Bourbon France, the curtailing of Habsburg ambition, and the ascendancy of Sweden as a Great Power created a new balance of power on the continent. The Dutch Republic also secured Spanish recognition of its independence after an 80-year revolt, leading to the Dutch Golden Age.