The Great Vowel Shift
The Middle English pronunciation will change radically beginning now. The average English-speaker of 1400 will be practically incomprehensible to the English-speaker of 1450. The long vowels are changing as people pronounce their vowels more up the throat. No one knows what precipitated the sudden change but modern vocalization begins at this time.  
An Historian Warns about History
A greater hazard, built into the very nature of recorded history, is overload of the negative [...] History is made by the documents that survive, and these lean heavily on crisis and calamity, crime and misbehavior [...] No Pope ever issued a Bull to approve of something.
-- from "A Distant Mirror: The Calamitous 14th Century" by Barbara Tuchman. 
History from the Middle Ages is also biased toward the aristocracy because the aristocracy are literate. That results in the peasants becoming the "villains" in any story told by the aristocracy. In fact, the modern word "villain" is a product of this bias. A villain is a man from the village. In other words... a peasant. It has turned into a negative word as the villagers have interacted more and more with the aristocracy.
This Year in Wikipedia
Year 1401, Wikipedia.
- Boren, James. (A professor teaching Chaucer at the University of Oregon) Great Vowel Shift Chart without Graphemes, 2014 [last update]. Note: This web page is Professor Boren's work adapted by Dr. L. Kip Wheeler.
- Wheeler, L. Kip. (A professor at Carson-Newman University) History of the English Language, 2014 [last update]
- Crichton, Michael. Timeline. New York: Alfred A. Knopf. 1999. bibliography. (NOVEL)
- Occitan language - Wikipedia, 2014 [last update]
- Tuchman, Barbara Wertheim. (Barbara Tuchman, bio). A Distant Mirror: The Calamitous 14th Century. Ballantine, 1979. p. xviii. "Forward" (BOOK)