 Complete the following phrase:  Upon the death of Byzantine Emperor John VIII Palaiologos in Constantinople in October 1448, the imperial throne fell to Constantine, who was crowned on 6 January 1449 in Mystras before departing for the capital. Two months later, he assumed his new role in Constantinople as Emperor Constantine XI. His younger brothers, Thomas and Demetrius remained in charge of the Morea as joint Despots in his place. Despite assurances to Constantine that they would pledge support to one another, both Thomas and Demetrius coveted the others lands  in addition, they pressed claims against Venetian port possessions in the Morea, alienating the only power capable of aiding them in resisting the Turks. The mutual hostility went to the point that both despots requested military aid from the Turks against the other. During the final 