The year 1066 is highly significant in the English language. This is the year that William, the Duke of Normandy, conquer most of what today is known as Great Britain. The effects of this upon the English language was significant.
As a background, when the King of England, Edward the Confessor died, he named William, the duke of Normandy, as King of England. Edward was childless but his mother was from Normandy, which is located in France. As such, the English court was already full of French speaking Normans as Edward’s supporters.
Naming a Norman to the throne of England did not sit well with one Edward’s biggest rivals, Earl Harold Godwineson. Harold quickly led a rebellion against Willam but was defeated and William of Normandy became known as William the Conqueror and was crowned King of England Christmas day of 1066
Over the next three centuries under French rule, the English language was invaded by as many as 10,000 French words. Such words as “city”, “bacon”, “biscuit”, and “felony” to name a few. The English court quickly became a French court.
The English court quickly became a French court. All positions of power were taken by Normans. This was not only because of conquest but also because most of the English nobility and leadership were killed in the Battle of Hastings.
The only way to get ahead in this context was to learn French and leave English in the home. In many ways, French became a high language and English was relegated to a low language almost as a diglossia situation. English was the language of the poor and French of the elite. Most documents during this time were produced in French and even written English was pushed aside.
The division by class has led some to allege that this kept English alive. This is to say that the rich and the poor had their own separate languages and both work to preserve their own manner of communication.
War is yet another factor to consider when looking at the development of a language. Even without intending to do so William the Conqueror made a major impact on the English language simply by sticking to his mother tongue of French when he took the English throne. To this day, loan words from French play a major role in communication in the English language.