Tuesday (September 11, 2018) marks the 17th anniversary of the cataclysmic jihad terror attacks in the United States on September 11, 2001. Thirteen centuries ago, on August 15, 718, under the wise and stalwart leadership of Byzantium’s Leo III, the Arab Muslim jihad siege of Constantinople was broken, and the invaders—and Islamdom—suffered an ignominious defeat. These events are described with unique lucidity and unbowdlerized knowledge of their animating Islamic and Christian motivations in Raymond Ibrahim’s compelling new book, Sword and Scimitar. Would that today’s U.S. and other “Western” leaders reconsider their largely feckless policies against the resurgent jihad depredations of...