The Saxon Fratricidal War was a war fought between the two brothers Frederick II, Elector of Saxony and Duke William III over Wettin ruled areas from 1446 to 1451. After a dispute over the division of certain family lands between Frederick II and William III, the Division of Altenburg eventually led to growing tensions between the two brothers and an inability to agree on who ruled which areas. After failed attempts at reconciliation, the war broke out and lasted for five years. The war was destructive and had no clear winner before being ended with a peace treaty at Naumburg. Following the war and subsequent divisions the Saxons lost much of their former power and influence within the different German states and families.

Frederick II, The Gentle was Elector of Saxony (1428–1464) and was Landgrave of Thuringia (1440–1445).