The ritual decapitation of 800 Christians who refused Islam 539 years ago—and whose commemoration was last Friday, August 14—sheds much light on contemporary questions concerning the ongoing conflict between Islam and the West. Background: When he sacked Constantinople in 1453, Ottoman Sultan Muhammad II was only 21-years-old—meaning he still had many good decades of jihading before him. He continued expanding into the Balkans, and, in his bid to feed his horses on the altar of Saint Peter’s basilica—Muslim prophecies held that “we will conquer Constantinople before we conquer Rome”—he invaded Italy and captured Otranto in 1480. More than half...