Gemistus Pletho
In 1439 the Byzantine Empire was on the verge of collapse, retaining little more than the city of Constantinople, as the Ottoman Empire swept into Europe. During the reign of John V Palaiologos in the preceding century, the Byzantine Emperor had issued pleas to the West for aid in exchange for a union of the Roman Catholic and Greek Orthodox churches; the Papacy had been unmoved by these appeals, as had been King Louis I of Hungary. In 1369, after the fall of Adrianople to the Ottomans, John V had again issued a plea for help, hastening to Rome and publicly converting to Roman Catholicism. Help had not come, and John V was instead forced to become a vassal of Ottoman Sultan Murad I. A brief respite from Ottoman control later came as Timur pressured the Ottomans on the east, but by the 1420s Byzantine Emperor John VIII Palaiologos again acutely felt the need for assistance from the West. He again made the same plea his predecessor had, travelling with a delegation to the Council of Ferrara-Florence to reconcile with the Western Church. He consulted with Neoplatonist philosopher Gemistus Pletho, who advised him that the Roman Catholic and Eastern Orthodox delegations should have equal voting power at the Council; nonetheless, the Emperor was under far more pressure to bring about a union than was the Pope. In order to help the Russian Orthodox Church unite with the Western Church, John VIII appointed Isidore of Kiev as Metropolitan of Kiev in 1436 against the wishes of Vasily II of Moscow.