William I (the Conqueror) made no attempt in his lifetime to combine all of his possessions into a single empire. At his death in 1087 he was Duke of Normandy and King of England; he left Normandy to Robert, and England to his second surviving son, William Rufus (William II).
Robert's reign as Duke of Normandy is noted for the discord with his brothers, each of whom came to the English throne as William II and Henry I respectively. Robert mortgaged his duchy to finance his participation in the First Crusade, where he was an important commander. His disagreements with Henry I led eventually to defeat in battle and lifelong captivity, with Normandy absorbed as a possession of England.
© Haydn Thompson 2020