First War of the Guelderian Succession

The First War of the Guelderian Succession was a battle for the throne of the Duchy of Guelders that raged between 1371 and 1379.

The war originated when Duke Reginald III died without issue on 4 December 1371. His brother, Edward, who had been killed in the Battle of Baesweiler earlier that same year, also left no offspring. The claimants to the ducal throne were their half-sisters: Mechtild who was married twice before but without offspring, and Mary, wife of William II of Jülich and mother to William I of Guelders and Jülich, on whose behalf she claimed the throne of Guelders.

During this conflict, the nobility and cities of 14th-century Guelders were divided in two factions, the Heeckerens and Bronckhorsters. This division had previously occurred during the Guelders Fratricidal War (1350-1361) between Edward and Reginald III. Both fractions were named after and led by a prominent Guelderian noble family.

• The Heeckerens supported Mechtild, and were led by Frederik van Heeckeren van der Eze (1320-1386).
• The Bronckhorsters supported William, and were led by Gijsbert V van Bronckhorst (1328-1356).

The war lasted eight years. In 1379, Mary and her supporters emerged victorious, with Mary's son William becoming the next duke of Guelders.