D-Day was a turning point for World War II because it completely flipped the tables on who was winning. Before this invasion, Germany was very powerful and kept sending troops to places like France, where they didn't have a way to push out the German troops.
Germany had no clue where this invasion would be coming from, even though they knew it would be happening. This was fantastic, as it made it so German troops wouldn't concentrate in the area where the Allies would be attacking from.
Several days past the initial attack of Normandy, numerous Allied troops were still making their way there. By the end, about half a million troops had arrived and began to successfully push the Germans out of France.
D-Day is known as the "beginning of the end" for Germany, as it was the turning point where Germany became weak. They could not handle the pressure and troops flooding in from separate directions and ended up losing France.
