One could draw an unbroken line between Chaucer's 14th-century language and the modern English we speak today. No wholesale alterations have swept through the language. No concerted efforts at overhaul brought about any particularly effective reforms.
Languages just change - gradually, almost imperceptibly.
No massacres need occur to kill a language, just a gradual decline in its use, as successive generations forget the old and embrace the new. Sometimes, in hindsight, the loss of a language comes to be viewed as a tragedy. The final speakers of a dialect make an effort to pass on the legacy of the language - the unique forms of expression that help to define a cultural heritage. Sometimes these efforts succeed to the extent that important texts are preserved, and professorial chairs are endowed. Other times, as with the Gaelic tongue in Ireland and certain Native American tongues in North America, younger generations learn the languages of their ancestors as a way of reconnecting with a culture they may have been on the verge of losing.