Why did Byzantine rulers discuss church union with Rome during the Ottoman threat?

Byzantine rulers pursued church union with Rome primarily as a political strategy to secure military assistance from Western Christendom against the encroaching Ottoman Turks.12

Throughout the Palaeologan period, as the empire’s territory dwindled, emperors hoped that submitting to the authority of the papacy would trigger a new Crusade or provide the necessary support to defend Constantinople. This policy was driven by political desperation rather than ecclesiastical consensus. Notable attempts included:12

• Council of Lyons (1274): Emperor Michael Palaeologus accepted union to gain papal support against the ambitions of Charles of Anjou.1
• Council of Ferrara-Florence (1438–1445): Faced with the existential threat posed by the Ottomans, Emperor John VIII Palaeologus and other leaders signed the Union of Florence in 1439, accepting Roman positions such as the Filioque clause and papal primacy.12

These efforts were deeply unpopular among the Byzantine populace and clergy, who remained committed to the Eastern Orthodox faith and harbored long-standing resentment toward the West following the Schism of 1054 and the 13th-century Latin occupation. Ultimately, the union failed to provide the substantial military aid required to prevent the fall of the empire.132