Here is Constantinople, the “City of Heraclius”, now Istanbul. The first city to be “opened” by Islam in Mohammedan prophecy. The next is Rome.
When Constantinople fell, Europe was cut off from the rest of the world and trade routes to the East were severed; whereas Islam had the world at its back, with room to grow and unlimited resources upon which to draw. Therefore it would have been only a matter of time before the entire continent fell. This forced the Europeans to seek a Westward outlet, which led to discovery of the Americas. Thus was Christendom saved.