A family feud between grandfather and grandson triggered the final decline of Byzantium
The Byzantine civil war of 1321–1328 began as a personal rift between Emperor Andronikos II and his grandson, Andronikos III. What started as a domestic struggle for control quickly exhausted the empire's resources, destabilized its economy, and left its Anatolian borders vulnerable to the rising Ottoman threat.
The conflict originated from a tragic accident in 1320, when Andronikos III inadvertently caused the death of his brother, Manuel. This event, coupled with the younger Andronikos's dissolute behavior, alienated him from his grandfather, Andronikos II. By Easter 1321, the younger Andronikos had fled to Adrianople, gathering support from aristocratic clans and initiating an uprising. The resulting peace agreements, including those in 1321 and 1322, failed to resolve the underlying power struggle, as both men pursued competing foreign policies and internal factions shifted allegiances.
By 1327, the war had expanded into a broader Balkan conflict, drawing in the Serbian king Stefan Dečanski and the Bulgarian emperor Michael Shishman. After securing Macedonia and Thessalonica, Andronikos III successfully entered Constantinople in May 1328, forcing his grandfather to abdicate. While the new government attempted to stabilize the legal system, the war had already inflicted severe damage, including reduced agricultural production and a drop in the value of money.
The most critical consequence was the collapse of Byzantine defenses in Anatolia. While the empire focused on internal strife, the Ottomans captured Prusa and besieged Nicea and Nicomedia. A subsequent attempt by Andronikos III to reverse these losses at the Battle of Pelekanon ended in a disastrous defeat. This failure effectively ended Byzantine power in the region. Historians view this civil war as the first domino in a sequence of events that ultimately led to the fall of Constantinople in 1453.
Source: Byzantine civil war of 1321–1328
