Byzantine civil war of 1373 – 79 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 major beneficiary of the war were the Ottomans , whose vassals the Byzantines had effectively become . Background . When John V assumed sole rule of the Empire in 1354 , he pursued a clearly pro - Western foreign policy . He gave Lesbos and his sister ' s hand in marriage to a Genoese , Pontic Heraclea , Byzantium ' s last Anatolian port , was sold to the Venetians , and he himself converted to Roman Catholicism , an action that alienated him from his subjects and gained little in return . By the 1360s , the Byzantine Empire was a shadow of its former self . Its last domains in Thrace were being overrun by the Ottomans , who in 1365 captured Adrianople ( modern Edirne ) . Seeking aid from the West , in 1369 John V visited Pope Urban V that summer , and following that he sailed to Venice , where he negotiated a treaty in which the Venetians would cancel the emperor ' s debt in return for the island of Tenedos . On leaving Byzantine soil he left his two sons , Andronikos IV and Manuel , to manage Constantinople and Thessalonica respectively . Andronikos IV , the elder son and co - emperor , however refused to hand over Tenedos to the Venetians as agreed , and the Emperor was detained by the Venetians for two years until Manuel intervened on his behalf . First conflict – Failed revolt of Andronikos IV , 1373 . Andronikos IV resented his father ' s acceptance of tributary and vassal status to the Ottoman Empire in 1373 , and in the same year , he joined Savcı Bey , a son of the Ottoman Sultan Murad I , in a joint open rebellion against their fathers . Both revolts were suppressed , although Byzantine military weakness meant that this was largely carried out by Turkish troops . Murad blinded ( and later executed ) Savcı and demanded that John V in turn blind both Andronikos and the latter ' s son , John , as well . John V did so only partially , leaving Andronikos IV with one eye and his grandson only partially blinded , but he did imprison Andronikos . The younger John greatly resented his grandfather ' s action and would rebel against him in 1390 , reigning for five months . In the aftermath of Andronikos ' failure , Manuel was raised to co - emperor and heir to John V as Manuel II . Second conflict – Andronikos ' usurpation , 1376 – 1379 . Shortly after Andronikos was imprisoned , John V sold Tenedos to the Venetians on similar terms to previous failed agreement . The Genoese however did not take kindly to the island being in the hands of the Venetians , with whom they were embroiled in a war . Thus , in 1376 , the Genoese , based in their colony in Galata , helped free Andronikos and procure Ottoman troops for him . Andronikos assumed control of Constantinople and imprisoned the Emperor John V and his younger brother Manuel . In return for their help , Andronikos IV now gave Tenedos to the Genoese and Gallipoli to the Ottomans . These acts in turn embroiled him , shortly after his accession , in a war with Venice . Together with his son , John VII , who was crowned as co - emperor in 1376 , there were now no less than four emperors in Byzantium , all of them more or less pawns in the policies of the Ottomans and the Italian city - states . Andronikos IV ruled until 1379 , when John V and Manuel II escaped and fled to the court of Murad I . After apparently agreeing to cede the virtually independent Byzantine exclave of Philadelphia to the Ottomans , John V was reestablished on the throne with the help of Venetian ships and the Ottoman army . Aftermath . After John V entered the capital , Constantinople , Andronikos IV fled to Genoese Galata and stayed there two years . However he held hostage for a time his mother , Helena Kantakouzene , and her father , the former emperor John VI Kantakouzenos . However in 1381 a treaty was signed in which allowed him to return . Later on the Venetians and Genoese ended their war and agreed to depopulate Tenedos and raze its fortifications , hence transforming it to a neutral territory . This conflict further weakened the Byzantine Empire , which was surrounded by the massive and ever - expanding Ottoman Empire .