As context, a summary of some events in the year leading up to the Fall of Constantinople:
Kuwae, a large volcano off Vanuatu in the Pacific erupts. The event released an enormous amount of sulfur and is credited with causing a global cooling event. It is also one explanation for the unusual and extreme weather conditions which blighted Constantinople in its final six months and gave rise to a tangible sense of doom.
Byzantine ambassador to Venice reports a massive build-up of Ottoman troops in preparation for an assault and begs assistance. He is told Venice has too much on her plate in Italy to commit to war with the Turks.
Frederik III was crowned Holy Roman Emperor in Rome. The first Habsburg Emperor, he would reign for almost 40 years.
Leonardo da Vinci born.
Mehmed begins work on his 'Throat Cutter' castle on the Bosporus.
War flares between Venice and Milan once again but although armies take to the field there is little open battle.
Philip the Good of Burgundy officially declared war on Ghent.
Pope Nicholas V issues the bull Dum Diversas which allowed for non-Christians to be enslaved in perpetuity. It was primarily a license for the Portuguese King Alphonso V to begin the trading of slaves on the newly discovered West Africa routes if they did not swiftly convert to Christianity.
Mehmed II launches his first campaign against Skanderbeg in Albania. The initial force of 25,000 men under Hamza Pasha and Tahip Pasha is split in two, allowing the swift, smaller Albanian forces to deal with each in turn.
Rumeli Hisar, The Throat Cutter, is completed, giving Ottoman guns full control of the Bosporus on the Black Sea side of Constantinople.
Venice dispatches Gabriel Trevisano to Constantinople in response to defend Venetian muda convoy from the Black Sea.
A motion is tabled in Venetian senate to officially abandon Constantinople to its fate. It is rejected.
Durad Brankovic attacks the Venetian city of Cattaro (Kotor)
Savanarola born in Ferrara
Isidore of Kiev arrives in Constantinople with a body guard of 200 Papal archers from Naples and Bishop Leonard of Chios. He is charged with officially overseeing the consecration of Hagia Sophia to the Latin creed and thus the consummation of the Union of the churches which is more of a submission of the Greek church into the Latin faith.
Birth of future Richard III of York
The Hundred Years War was drawing to a close. England sent troops under John Talbot to Guyene (Bordeaux).
Turukhan Beg, Ottoman governor of Thessaly breaks the Hexamilion wall at the Isthmus of Corinth and raids the Peloponnese.
Byzantine ambassador in Venice is officially told that he should take his plea for aid to the Pope and that Venice had her own contingency plans. It is as close to an official abandonment as la Serenissima will make.
12th of December. Isidore conducts the official ceremony that consecrates Hagia Sophia as a Latin cathedral. It is abandoned from that day by the populace of Constantinople until the eve of its fall in May 1453.
Grand Pricne Vasily of Moscow establishes the Qasim (Kasimov) Khanate as a buffer client-state between his territory and the Khanate of Kazan. Qasim is one of Ghengis Khan's (many) grandsons. His Tatars will fight for Moscow and conduct raids into Kazan.