To understand the political situation in Europe during the reign of Vlad the Impaler, we need to go back in time and examine an event that took place during the reign of his father, in 1439.

The council of Florence was a meeting of bishops, cardinals, metropolitans and patriarchs where they discussed the growing threat represented by the advancement of Mehmed the 2nd [currently the most commonly used name the Sultan is “Mohammed”, but this leaves room for confusion regarding the true identity of those who ruled the Ottoman Empire] in the midst of Europe.
Recognizing the seriousness of the problem, the Pope of Rome and the Patriarch of Constantinople came to an agreement to end their fut. Even John Palaiologos was convinced that only an association with the Catholic empire – then the richest and most powerful in the whole continent – could save his Imperial town.
Unfortunately this agreement was brought to an end because on the way back to Constantinople the Patriarch died, and the newly elected one was influenced by bishops not to accept the union with Rome.
The document signed in the council of Florence was not recognized!
As the emperor feared, Constantinople fell after a siege of only two months and it became the new capital of the Ottoman Empire!
But the were still knights present and willing to support the crusade begun by the Pope, among them: John Hunyadi, Vlad Dracul, and later their sons – Matthias Corvinus and Vlad the Impaler!

๑۞๑ Related:๑۞๑
† Vlad the Impaler
† Count Dracula