Thomas Cahill has a book, 'How the Irish Saved Civilization,the Untold Story of Ireland's Heroic Role from the Fall of Rome to the Rise of Medieval Europe'.
This article states some of the exact points Mr. Cahill made is his discription of Rome's failures.
Medieval Muslims effectively cut of the land routes to the far east that had been used for centuries and closed the Mediterranean to trade with their pirates. That stimulated the search for new trade routes.