John VIII (John Palaeologus), 1390–1448, Byzantine emperor (1425–48), son and successor of Manuel II. When he acceded, the Byzantine Empire had been reduced by the Turks to the city of Constantinople. John sought in vain to secure Western aid by agreeing at the Council of Florence (1439) to the union of the Eastern and Western churches. His brother, Constantine XI, succeeded him in 1449 and was the last Byzantine emperor.
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