Here are some key factors:
* The printing press (mid-15th century): This greatly standardized spelling and grammar, pushing the language towards a more consistent form.
* The Great Vowel Shift (14th-18th centuries): This dramatic shift in pronunciation further differentiated Early Modern English from Middle English.
* The Renaissance (14th-16th centuries): This period brought renewed interest in classical learning, which influenced vocabulary and syntax.
* The Reformation (16th century): Religious changes also had a significant impact on the language, particularly with the widespread translation of the Bible.
While historians generally agree that Middle English ended sometime between 1485 (the end of the Wars of the Roses) and 1603 (the death of Queen Elizabeth I), it's important to remember that the process of change was gradual and regional variations persisted.
Ultimately, the transition between Middle English and Early Modern English was not a sudden event but a long, gradual process.