It must be remembered also that the Eastern Church had steadily refused to admit the supremacy of the Western. It had never regarded the phrase ‘under one fold and one shepherd’ as indicating that the whole Church of Christ should be under the government of one bishop. It had never admitted that the ‘One Shepherd’ should be other than Christ, and had therefore constantly denied the supremacy of the pope. One Empire, one Church, one Head of the Church was a Western theory which had never made much way in the later Roman empire. The movements in the West which placed the imperial power in commission, giving to the emperor the supreme secular, and to the bishop of Rome the supreme ecclesiastical, authority had no corresponding movement in the East. The emperors were only heads of the Church in the same sense as the king of England is in all matters ecclesiastical supreme. The emperors and ecclesiastics were usually agreed in not allowing the supremacy of the bishop of the elder Rome. To the popes, however, the Union of the Churches was indissolubly associated with the admission of papal supremacy. It would be going too far to say that they desired Union exclusively to obtain recognition of such supremacy, but it may safely be said that they never lost sight in all their negotiations for Union of the necessity of obtaining its recognition, and that, in the opinion of many ecclesiastics both Western and Eastern, such supremacy was the most important object aimed at. Murad’s unsuccessful attempt, in 1422, to capture Constantinople made it evident to the emperor that aid from Western nations was absolutely necessary if the empire or even the city was to be saved. The pope also recognised both the importance of saving the empire and its extreme danger, and held out hopes of aid if Union were accepted. The imminence of the danger was patent to all. When John became sole occupant of the throne, in 1425, the empire was surrounded by Turkish armies. Nearly the whole of Asia Minor was in their hands. Large armies had invaded Hungary; Bulgaria had ceased to exist; Serbia was a vassal of the sultan. In Macedonia and even in Thrace the Turks had made a desolation and held many cities. If the city of Paris were worth a Mass, the empire was worth a tenfold acknowledgment of the pope’s supremacy. The emperor, the nobles, and a considerable part of the clergy came to believe that they must purchase aid on any conditions or see the city captured. Questions of dogma, the addition of the _Filioque_ clause, the use of unleavened bread, the condition of souls in purgatory, were to them matters of secondary importance when the very existence of their country was at stake. Even papal supremacy appeared to John and many laymen worth accepting in return for the despatch of soldiers who would resist the Turkish invasion.