The Thirty Years' War from 1618 to 1648 was one of the most destructive wars in European history. An estimated 4.5 to 8 million soldiers and civilians died as a direct result, while some areas of present day Germany experienced population declines of over 50%. Related conflicts include the Eighty Years' War, the War of the Mantuan Succession, the Franco-Spanish War, and the Portuguese Restoration War.
Until the 20th century, the conflict was seen as part of the German religious struggle which was initiated by the 16th-century Reformation. The 1555 Peace of Augsburg divided the Holy Roman Empire into Lutheran and Catholic states, but over the next 50 years, the expansion of Protestantism beyond these boundaries destabilized Imperial authority. Although religion was a significant factor in the outbreak of the war, scholars generally believe its scope and extent were driven by the contest for European dominance between the Habsburgs in Austria, Spain, and the French House of Bourbon.
The war began in 1618 when Ferdinand II was deposed as King of Bohemia and replaced by Frederick V of the Palatinate. Although the Bohemian Revolt was quickly suppressed, fighting expanded into the Palatinate, whose strategic importance drew in the Dutch Republic and Spain, then engaged in the Eighty Years' War. Since ambitious external rulers like Christian IV of Denmark and Gustavus Adolphus of Sweden also held territories within the Empire, they joined the fighting at various intervals. Repeated foreign intervention transformed what began as an internal dynastic dispute into a far more destructive Europe-wide conflict.
The first phase of the war, which lasted from 1618 until 1635, was primarily a civil war between German members of the Holy Roman Empire with external powers playing supportive roles. After 1635, the Empire became one theatre in a wider struggle between France, supported by Sweden, and Emperor Ferdinand III, allied with Spain. This concluded with the 1648 Peace of Westphalia, whose provisions included greater autonomy within the Empire for states like Bavaria and Saxony, as well as acceptance of Dutch independence by Spain. By weakening the Habsburgs relative to France, the conflict altered the European balance of power and set the stage for the wars of Louis XIV.
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