The event that began the transition from Old English
to Middle English was the Norman Conquest of 1066,
when William the Conqueror (Duke of Normandy and,
later, William I of England) invaded the island of
Britain from his home base in northern France, and
settled in his new acquisition along with his nobles
and court. William crushed the opposition with a
brutal hand and deprived the AngloSaxon
earls of
their property, distributing it to Normans (and some
English) who supported him.