The Byzantine civil war of 1373–1379 was a military conflict fought in the Byzantine Empire between Byzantine Emperor John V Palaiologos and his son, Andronikos IV Palaiologos, also growing into an Ottoman civil war as well, when Savcı Bey, the son of Ottoman Emperor Murad I joined Andronikos in a joint rebellion against their fathers. It began when Andronikos sought to overthrow his father in 1373. Although he failed, with Genoese aid, Andronikos was eventually able to overthrow and imprison John V in 1376. In 1379 however, John V escaped and, with Ottoman help, regained his throne. The civil war further weakened the declining Byzantine Empire, which had already suffered several devastating civil wars earlier in the century. The primary beneficiary of the war were the Ottomans, as the Byzantines became their vassals.

Manuel II Palaiologos or Palaeologus was Byzantine emperor from 1391 to 1425. Shortly before his death he was tonsured a monk and received the name Matthew. His wife Helena Dragaš saw to it that their sons, John VIII and Constantine XI, became emperors. He is commemorated by the Greek Orthodox Church on July 21.