The conquest of the Byzantine capital Constantinople by the Ottoman army under Sultan Mehmed II (1432–1481) sealed the fate of the Byzantine Empire and triggered the feeling of an immediate, existential threat emanating from the Ottoman Empire.
Conquest of Constantinople by the Turks, 29 May 1453. The Turkish army before Constantinople, illumination, 1455, from the workshop of Jean Mielot. Illustration of: Avis directif pour faire la passage d'Outremers. Mss. français 9087, fol. 307 v; image source: akg-images, image number: 9TK-1453-5-29-A1-1.