Guyuk Khan vs John VIII Palaiologos

Güyük was elected as the third Great Khan of the Mongol Empire at a kurultai near the Mongol capital Karakorum. His election was supported by his mother Töregene, who had served as regent, but was opposed by Batu, leading to tensions.

Güyük received the Franciscan envoy John of Plano Carpini at his court, who delivered a letter from Pope Innocent IV demanding the Mongols cease their invasions. Güyük's reply demanded the Pope's submission to Mongol authority, reflecting Mongol imperial ideology.

Güyük planned a military campaign against his cousin Batu, ruler of the Golden Horde, due to Batu's refusal to recognize his authority. The conflict was averted when Güyük died in 1248, but it deepened the rift between the Toluid and Jochid lines.

Güyük died suddenly in 1248 while marching west to confront Batu, possibly poisoned. His death left the empire without a clear successor, leading to a regency by his widow Oghul Qaimish and eventually the election of Möngke in 1251.

John VIII traveled to Italy with a large delegation of Orthodox clergy to participate in the Council of Florence, which aimed to negotiate church union. His presence underscored the Byzantine Empire's desperation for Western aid.

John VIII Palaiologos, as Byzantine emperor, agreed to the Union of Florence, which temporarily reunited the Eastern Orthodox Church with the Roman Catholic Church under papal authority. This was done to secure Western military aid against the Ottoman Empire, but the union was widely rejected by the Byzantine populace and clergy.

John VIII died embittered, having failed to secure effective Western military support despite the Union of Florence. The Ottoman Empire continued its conquests, and the union deepened internal divisions within Byzantium.