he union of the Eastern and Western Churches signed at the Council of Ferrara and Florence in 1439 following Byzantium's plea for help to the Western powers and the Pope, was not accepted by the majority of the Byzantine people and gave rise to conflicts within the state. What is more, it was of no immediate political benefit to Byzantium, since no military help was sent. All the Pope did was summon the Christian West to a crusade against Islam, particularly after the victories of Janos Hunyadi, the voivod of Transylvania, against the Turks in Serbia and Wallachia.

To this summons the Christian sovereigns responded willingly, the more so since the crusade was favoured at this moment by the victorious advance of Constantine, who, having subdued the Duke of Athens, Nerio II, and made him his tributary, had conquered Phokis and extended his rule as far north as the Pindos mountains(1440). At the same time, the Albanian patriot, George Kastriota Skanderberg, had stirred up his compatriots, who had risen up in revolt against the Turks. Circumstances were favourable. The crusade was launched in July 1443. 25,000 crusaders took part under the leadership of the King of Hungary, Ladislas III, George Brankovic of Serbia and the Hungarian nobleman Janos Hunyadi. Things were going well for the crusaders, who, by November 1443 had taken Naissus and Sofia. In June 1444 their delegates came to an understanding with Murad II and the two parties signed a ten-year truce. Influenced by Cardinal Juliano Cesarini, Ladislas decided to continue the crusade notwithstanding. However, in November 1444, at Varna, the crusaders suffered a crushing defeat and both Ladislas and Cardinal Cesarini were killed in the battle. This defeat marked the definite dominance of the Turks in south-eastern Europe.