The War of the Lüneburg Succession () was a conflict over the succession to the Principality of Lüneburg that broke out in 1370 in north Germany and lasted, with interruptions, for 18 years. After William II of Lüneburg died without male heirs in 1369, the "Older House of Lüneburg" was extinguished. According to the inheritance rules of the House of Welf to which William belonged, the Duke of Brunswick, Magnus II Torquatus, was entitled to succeed. However, Charles IV ruled that this Imperial Fief should be returned to the Empire and enfeoffed Albert of Saxe-Wittenberg and his uncle, Wenceslas with the Principality, thereby triggering the war.
The town of Lüneburg supported the Wittenbergs, taking the opportunity to escape from the immediate lordship of the Duke, and destroyed the ducal castle on the Kalkberg on 1 February 1371. This forced the Duke to relocate his residence to Celle. An attempt on 21 October 1371, Saint Ursula's day, to defeat Lüneburg militarily and reinstate the old ducal rights failed. During the military conflict in the years that followed, neither the Brunswicks nor the Wittenbergs were able to assert their claims, and it was only through the Peace of Hanover in 1373 that the war came to an end, at least for the time being.
In accordance with the agreements reached at Hanover, the regency would alternate between the Welfs and the Wittenbergs. The treaty was further reinforced by the marriage of the two eldest sons of Magnus Torquatus, Frederick and Bernard I, to the two daughters of Wenceslas, as well as the marriage of Magnus's widow to Albert of Saxe-Wittenberg. Henry, the younger brother of Frederick and Bernard, however, rejected the agreements and continued the war. After the Battle of Winsen in 1388, when Wenceslas lost his life, possibly a result of poisoning, rule over the Principality was assumed by the House of Welf, in accordance with the provisions of the Treaty of Hanover, dating from 1374. In 1389, a treaty of inheritance between the Welfs and the Ascanians was concluded, the 1374 treaty was abolished and the Principality was finally secured for the Welfs.
Background
In 1355, the Duke of Lüneburg married his daughter Mechtild to her cousin Louis, the heir to the throne in the Principality of Brunswick, and appointed him as his heir and successor in Lüneburg. In the event that Louis predeceased him, William retained the right to choose a successor from his brothers. In the same year, however, Emperor Charles IV guaranteed the succession of Lüneburg on the death of William, who had no sons, to the Ascanian dukes of Wittenberg in the form of an Eventualbelehnung, a fief contingent on the death of William. Charles IV rejected the female inheritance law and regarded the fief, on the death of William, as returning to the Empire. The official appointment of William to the dukedom in 1235, in which the cognatic succession had been assured, led to further negotiations between the Duke and the Emperor, but these did not reach a conclusion. The assessment of earlier research that assumed William had originally supported the contingent enfeoffment of Albert of Saxe-Wittenberg, is regarded as unfounded in more recent research. When Louis died in 1367, William appointed his brother Magnus II as his successor and made him his co-regent in the same year. When William died two years later, the Wittenbergs reaffirmed their claims to the Principality and Emperor Charles IV enfeoffed Duke Albert, his uncle Rudolf, who died shortly thereafter, and Wenceslas with Lüneburg.