The Heilbronn League was formed in the Free Imperial City of Heilbronn, on 23 April 1633, during the Thirty Years' War. Led by Sweden, it brought together various Protestant states in western and northern Germany. It was supported by Saxony and Brandenburg-Prussia, although they were not members.

The Battle of Lützen, fought on 6 November 1632, is considered one of the most important battles of the Thirty Years' War. Led by the Swedish king Gustavus Adolphus, an Allied army primarily composed of troops from Sweden, Saxony, and Hesse-Kassel, narrowly defeated an Imperial force under Albrecht von Wallenstein. Both sides suffered heavy casualties, with Gustavus himself among the dead.