By 1351 the Byzantine civil war was over, and John VI Kantakouzenos had realized the threat posed by the Ottomans to the Balkan Peninsula. He appealed to the rulers of Serbia and Bulgaria for a united effort against the Turks and asked Ivan Alexander for money to construct warships, but his appeals fell on deaf ears as his neighbours distrusted his intentions. A new attempt for cooperation between Bulgaria and the Byzantine Empire followed in 1355, after John VI Kantakouzenos had been forced to abdicate and John V Palaiologos had been established as supreme emperor. To cement the treaty, Ivan Alexander's daughter Keraca Marija was married off to the future Byzantine Emperor Andronikos IV Palaiologos, but the alliance failed to produce concrete results.