Complex sentence: Anglo-Norman and French relations became complicated after the Norman Conquest, as the Norman dukes retained control of their holdings in Normandy as vassals owing fealty to the King of France, but were his equals as Kings of England.
Split into simpler sentences: Anglo-Norman and French relations became complicated after the Norman Conquest. The Norman dukes retained control of their holdings in Normandy as vassals owing fealty to the King of France, but they were his equals as Kings of England.