Lack of stability was eminent in the southern Balkans as well : in 1341–1347 the Byzantine Empire was shaken Motion by a bloody civil war between John V Palaiologos and John VI Kantakouzenos .

During the civil war in Byzantium both Palaiologos and Kantakouzenos were trying to find external allies and used Using foreign mercenaries .

The Byzantine Emperor Michael VIII Palaiologos tried to exploit Control this situation to his favour and intervened Hindering in Bulgaria .

The attackers Attack were commanded Control by the 21-year-old Sultan Mehmed II , who defeated Conquering an army commanded Control by Emperor Constantine XI Palaiologos and took Getting control Control of the imperial capital , ending Process_end a 53-day siege Besieging that had begun Process_start on 6 April 1453 .

In 1378 Manuel II Palaiologos promised Commitment to hand over Giving the city of Philadelphia to the Turks in return for the Ottoman sultan 's aid Assistance in a disastrous Catastrophe Byzantine civil war .