I've been reading John Man's book
Gutenberg: How One Man Remade the World with Words
New York: MJF Books, 2002.
John Man says "29 May 1453 . . . was the birthday of the Renaissance" (Man, 2002, p. 231).
Here's John Man's hypothesis:
"Venice was printing capital not simply of Italy but of all Europe, with 150 presses. Success came for many reasons. . . . It was beautifully positioned for land and sea commerce, which it exploited to make itself Europe's richest city. And it had within reach of its ships the Greek-speaking world of Byzantium [Constantinople].Thus, when the Turks seized Constantinople in 1453 and turned it into Istanbul, it was to Venice that its scholars fled, forming a community of expatriate academics, La scuola e la nazione greca and creating an irony. The Fall of Constantinople was a notorious disaster for Christendom; yet it contributed to a boom in scholarship in Europe. The date 29 May 1453 [when the Turks took Constantinople] . . . was the birthday of the Renaissance . . .
...........
The influx of Greeks and their manuscripts fuelled a feeling among Renaissance scholars and artists that, in their search for classical antecedents, they had better explore their pre-Latin roots among the writings of the ancient Greeks. [Man, 2002, p. 231]
John Man sees this as a positive outcome of what some see as a negative,
an example of the so-called Law of Unintended Consequences -- good things can come from bad events,
and vice versa.
The key insight isn't that good came of the Fall of Constantinople. The key insight
is that knowledge moved when knowledgeable people moved. It's information transfer,
to new conditions, that fed the renaissance fires that were already burning brightly in Italy.