The fall of Constantinople by the Ottomans in 1453 A. D., led to the collapse of Byzantine Empire, which was considered one of the most powerful empires throughout history, after it had ruled vast parts of the Near East and Middle European countries for more than eleven centuries. Its collapse paved the way before Muslims to enter and possess large areas of lands and properties of the Christian Eastern Europe, and enabled the Ottomans to reach the heart of Europe, which made the entire Western Europe under the Islamic threat. The papacy was of the most European parties aware of that imminent danger, so it well prepared to confront the Islamic threat through forming anti-military religious Christian western alliance in parallel with recruiting all the papacy and European forces to support the Christian kingdoms in Spain financially, humanly, religiously and morally, so as to eliminate the Islamic presence in Al-Andalus homeland, subsequently to compensate the losses incurred by the Christians in the East, and this was achieved in 1492 A. D., when the Spaniards, with the help of the papacy, ended the rule of Granada, the last islamic kingdom in Al-Andalus.
"Crusader Papal - Spanish Policy toward Al-Andalus after fall of Constantinople (1453-1492 A. D.\857-897 A. H.),"
An-Najah University Journal for Research - B (Humanities): Vol. 30:
1, Article 7.
Available at: https://digitalcommons.aaru.edu.jo/anujr_b/vol30/iss1/7