Years ago I visited the site of the battle of Hastings and learned about it's significance to the English language, but I have always been curious how the transformation occurred. Did William the Conquerer directly and intentionally change the language, or was it a gradual process that developed over time? How did the common people adjust to the change? (More to do with etymology) Are there words we can directly trace back to the battle?
/u/Supalor answered your question in a blast from the past here.