The most celebrated church union was the Union of Florence in 1439. At this time the political atmosphere in the Christian East was much more critical than at the time of John's conversion. The sack of Serbia and Bulgaria by the Turks, the defeat of the crusaders at Nicopolis, the fruitless journey of Manuel II through western Europe, and finally the conquest of Thessalonica by the Turks in 1430, had put the Eastern Empire in a situation too critical to be saved by the Mongol defeat of the Turks at Angora. The Turkish successes were already a serious menace to Europe also; this was the reason why at the Council of Florence the necessity of a common Latin-Greek struggle against the Turks was so strongly felt. But in spite of the desperate situation, the Orthodox nationalistic party in Byzantium opposed the idea of union, not only from the fear of losing the purity of Greek Orthodoxy, but also from the feeling that western aid bought by the price of union would result in the political supremacy of the West over the East: in other words, the impending domination of the Turks might be replaced by that of the Latins. At the beginning of the fifteenth century, a Byzantine polemist, Joseph Bryennius, wrote; Let no one be deceived by delusive hopes that the Italian allied troops will sooner or later come to us. But if they do pretend to rise to defend us, they will take arms in order to destroy our city, race, and name. In the fifteenth century, this apprehension was justified by the political plans of Alfonso the Magnanimous against the East.
Elpenor's note : Vasilief's claim of a 'nationalistic' party against western help, is as absurd as the other claim, that Bryennius' apprehension was justified by the political plans of Alfonso. Bryennius and the Orthodox (not nationalistic) refusal of a religious union with the
Catholics is rooted in 1204, the atrocities of the Crusaders against Byzantium, the imposition of Latin clergy on the Greeks and the overall authoritarian mentality of papacy, together with what was understood by the Orthodox as papal heresies. Therefore, it is not a nationalistic reaction, but just common sense and defense of Orthodoxy. The ages that followed confirmed the anti-latin majority of the Byzantines, since (it is generally admitted) Orthodox peoples have kept their faith under so many difficulties, while western and westernised peoples have stooped to atheism.