The Norman Conquest of 1066 is perhaps one of the most debated events in history. Because of the outcome of one battle, Hastings, England became more involved in the tumultuous political atmosphere of continental Europe; English language and culture became forever scarred from French influence; and the kings of England (William, and his descendants, the Plantagenets), while ruling their kingdom, would, due to feudal complications, still be considered vassals to the King of France as Duke of Normandy. It is not so much the results of the Conquest that are debated but the course of the event itself: namely, to explain why William won, why Harold lost, and what means were taken by each side.
Pierlott, Collin J., "1066: The Norman Conquest" (2017). Undergraduate Research. 19.