Faced with the Ottoman danger, Michael's successors, prominently John V and Manuel II, periodically attempted to restore the Union, much to the dismay of their subjects. At the Council of Florence in 1439, Emperor John VIII reaffirmed the Union in the light of imminent Turkish attacks on what little remained of his empire. To the Byzantine citizens themselves, the Union of the Churches, which had assured the promise of a great western crusade against the Ottomans, was a death warrant for their empire. John VIII had betrayed their faith and as such their entire imperial ideology and world view. The promised crusade, the fruit of John VIII's labor, ended only in disaster as it was defeated by the Turks at the Battle of Varna in 1444.