Editing Constantine XI Palaiologos (section)

=== Search for allies ===
[[File:Eastern Mediterranean 1450.svg|left|thumb|Political map of the eastern [[Mediterranean Sea|Mediterranean]] in 1450]]
Shortly after Murad II's death, Constantine was quick to send envoys to the new Sultan Mehmed II in an attempt to arrange a new truce. Mehmed supposedly received Constantine's envoys with great respect and put their minds to rest through swearing by [[Allah]], the Prophet [[Muhammad]], the [[Quran]], and the [[angel]]s and [[archangel]]s that he would live in peace with the Byzantines and their emperor for the rest of his life. Constantine was unconvinced and suspected that Mehmed's mood could abruptly change in the future. In order to prepare for the future possibility of Ottoman attack, Constantine needed to secure alliances and the most powerful realms that might be inclined to aid him were in the West.{{Sfn|Nicol|1992|p=|pp=47–48}}

The nearest and most concerned potential ally was Venice, which operated a large commercial colony in their quarter of Constantinople. However, the Venetians were not to be trusted. During the first few months of his rule as emperor, Constantine had raised the taxes on the goods the Venetians imported to Constantinople since the imperial treasury was nearly empty and funds had to be raised through some means. In August 1450, the Venetians had threatened to transfer their trade to another port, perhaps one under Ottoman control, and despite Constantine writing to the [[Doge of Venice]], [[Francesco Foscari]], in October 1450, the Venetians were unconvinced and signed a formal treaty with Mehmed II in 1451. To annoy the Venetians, Constantine attempted to seal a deal with the [[Republic of Ragusa]] in 1451, offering them a place to trade in Constantinople with limited tax concessions, though the Ragusans could offer little military aid to the empire.{{Sfn|Nicol|1992|p=48|pp=}}

Most of the kingdoms in Western Europe were occupied with their own wars at the time and the crushing defeat at the Battle of Varna had quelled most of the crusading spirit. The news that Murad II had died and been succeeded by his young son also lulled the western Europeans into a false sense of security. To the papacy, the Union of the Churches was a far more pressing concern than the threat of Ottoman attack. In August 1451, Constantine's ambassador [[Andronikos Bryennios Leontaris]] arrived in Rome to deliver a letter to [[Pope Nicholas V]], which contained a statement from the anti-unionist ''synaxis'' at Constantinople. Constantine hoped that the Pope would read the letter and understand Constantine's difficulties with making the Union of the Churches a reality in the east. The letter contained the ''synaxis''<nowiki/>'s proposal that a new council be held at Constantinople, with an equal number of representatives from both churches (since the Orthodox had been heavily outnumbered at the previous council). On 27 September, Nicholas V replied to Constantine after he heard that the unionist Patriarch Gregory III had resigned following the opposition against him. Nicholas V merely wrote that Constantine had to try harder to convince his people and clergy and that the price of further military aid from the west was full acceptance of the union achieved at Florence; the name of the Pope had to be commemorated in the churches in Greece and Gregory III had to be reinstated as patriarch. The ultimatum was a setback for Constantine, who had done his best to enforce the union without inciting riots in Constantinople. The Pope appeared to have completely ignored the sentiment of the anti-unionist ''synaxis''. Nicholas V sent a [[papal legate]], Cardinal [[Isidore of Kiev]], to Constantinople to attempt to help Constantine enforce the union, but Isidore did not arrive until October 1452, when the city faced more pressing concerns.{{Sfn|Nicol|1992|p=|pp=49–51}}