The Thirty Years' War, a religious war fought over a thirty-year time period from 1618 to 1648, involving most of the major European powers, mainly takes place in the territory of Germany.

Beginning as a religious conflict between Protestants and Catholics in the Holy Roman Empire, it gradually develops into a general war involving much of Europe, for reasons not necessarily related to religion.

The war marks the culmination of the France-Habsburg rivalry for preeminence in Europe, which will lead to further wars between France and the Habsburg powers.The major impact of the Thirty Years' War, in which mercenary armies are extensively used, is the devastation of entire regions scavenged bare by the foraging armies.

Episodes of widespread famine and disease devastate the population of the German states and, to a lesser extent, the Low Countries and Italy, while bankrupting many of the powers involved.

The war may have lasted for 30 years, but the conflicts that triggered it are to continue unresolved for a much longer time.

The war ends with the treaties of Osnabrück and Münster, a part of the wider Peace of Westphalia.

Over the course of the war, the population of the German states is reduced by about 30%.

In the territory of Brandenburg, the losses amount to half, while in some areas an estimated two-thirds of the population dies.

The male population of the German states is reduced by almost half.

The population of the Czech lands declines by a third.

The Swedish armies alone destroy 2,000 castles, 18,000 villages and 1,500 towns in Germany, one-third of all German towns.