https://www.americanthinker.com/articles/2020/05/today_in_history_sword_of_islam_conquers_ancient_christian_capital.html
Today in history, on May 29, 1453, the sword of Islam conquered Constantinople. Of all Islam’s conquests of Christian territory, this was by far the most symbolically significant. Not only was Constantinople a living and direct extension of the old Roman Empire and contemporary capital of the Christian Roman Empire (or Byzantium), but its cyclopean walls had prevented Islam from entering Europe through its eastern doorway for the previous seven centuries, beginning with the First Arab Siege of Constantinople (674–678). Indeed, as Byzantine historian John Julius Norwich puts it, “[h]ad the Saracens captured Constantinople in the seventh century rather than the fifteenth, all Europe — and America — might be Muslim today.”
When Muslim forces failed again in the Second Arab Siege of Constantinople (717–718), conquering the ancient Christian capital became something of an obsession for a succession of caliphates and sultanates. However, it was only with the rise of the Ottoman sultanate — so named after its eponymous Turkic founder, Osman (b. 1258) — that conquering the city, which was arguably better fortified than any other in the world, became a possibility, not least thanks to the concomitant spread of gunpowder and cannons from China to Eurasia. By 1400, his descendants had managed to invade and conquer a significant portion of the southern Balkans — thereby isolating and essentially turning Constantinople into a Christian island in an Islamic sea.