War of the Mantuan Succession in the context of "Casale Monferrato"

The Thirty Years' War, fought primarily in Central Europe between 1618 and 1648, was one of the most destructive conflicts in human history. An estimated 4.5 to 8 million soldiers and civilians died from the effects of battle, famine, or disease, with parts of Germany reporting population declines of over 50%. Related conflicts include the Eighty Years' War, the War of the Mantuan Succession, the Franco-Spanish War, the Torstenson War, the Dutch–Portuguese War, and the Portuguese Restoration War.

Its causes derived from religious conflict within the Holy Roman Empire, sparked by the 16th-century Reformation. The 1555 Peace of Augsburg attempted to resolve this by dividing the Empire into Catholic and Lutheran states, but was later destabilised by the expansion of Protestantism beyond these boundaries. Combined with disagreements over the limits of imperial authority, religion was thus an important factor in starting the war. However, its scope and extent was largely the consequence of external drivers such as the French–Habsburg rivalry and the Dutch Revolt.

The term French–Habsburg rivalry (French: Rivalité franco-habsbourgeoise; German: Habsburgisch-französischer Gegensatz) describes the rivalry between France and the House of Habsburg. The Habsburgs headed an expansive and evolving empire that included, at various times, the Holy Roman Empire, the Spanish Empire, Portugal through Iberian Union, Austria, Bohemia and Hungary from the Diet of Augsburg in the High Middle Ages until the dissolution of the monarchy following World War I in the late modern period.

In addition to holding the Austrian hereditary lands, the Habsburg dynasty ruled the Low Countries (1482–1794), Spain (1504–1700) and the Holy Roman Empire (1438–1806). All these lands were in personal union under Emperor Charles V. The expansion of the Habsburgs into western Europe increasingly led to border tensions with the Kingdom of France, which found itself encircled by Habsburg territory. The subsequent rivalry between the two powers became a cause for several conflicts. These include parts of the Anglo-French Wars (1066–1815), the War of the Burgundian Succession (1477–1482), the Italian Wars (1494–1559), the Thirty Years' War (1618–1648), the Nine Years' War (1688–1697), and the succession wars of Jülich (1609–1614), Mantua (1628–1631), Spain (1700–1713), Poland (1733–1736) and Austria (1740–1748).