he union of the Churches (1274) imposed on the Byzantine people by Michael in his desire to further his foreign policy, was not to last long. Besides the adverse reaction within the Empire, Michael also faced strong opposition from the rulers of Thessaly and Epiros, who now set themselves up as the defenders of Orthodoxy. The factor, however, that actually brought about the failure of Michael's plans for Church union, was the change in papal policy.

After the death of Pope Gregory X (1271-76), his successor Nicholas III (1277-80) promoted the policy of union, even though he seemed to doubt the ability of Michael VIII to impose this union on the people of Byzantium. The next Pope, however, Martin IV (1281-1285), a Frenchman and a supporter of Charles I of Anjou and of his plans with regard to the conquest of Byzantium, did not follow the same policy of union as his predecessors. Instead, he favoured the signing, in July 1281, by Charles I of Anjou, the doge of Venice and the titular emperor of Constantinople, Philip of Courtenay, of the treaty of Orvieto, which was aimed against Byzantium.

Everything seemed to indicate that the Western forces, united once again, would soon deliver the mortal blow to the Byzantine Empire. Yet, this time again, the diplomatic genius of Michael VIII saved the day. During the uprising that he himself had incited in Sicily, in March 1282, and which came to be known as the Sicilian Vespers because it had started in Palermo with the ringing of the bells for vespers, his Sicilian rival was defeated and the Empire breathed once more. Not long afterwards, the man who had restored the Empire was to die, leaving the throne to his son, Andronikos II.