Historians think middle ages ended at the fall of Constantinople. From then on progress towards the modern world was swift.
The fall of Constantinople was more a matter that a variety of more advanced societies (Venice, the Turks, etc) were rising and the Byzantines were there, so why not loot them, as far as I understand the situation.
https://web.archive.org/web/20030930225420/http://www.the-or...
Personally I credit the printing press as the dividing line (yes I know the fall of Constantinople was at the same time).
Sometimes I idly think what would I invent if I was transported via mcguffin to ancient Rome. I'd invent paper and the printing press.