D-Day was an important victory for the Allies in World War II because it was the turning point of the war and showed how powerful the Allies really were.
D-Day, or the Invasion of Normandy, occurred on June 6, 1944. The Allies wanted to invade Normandy and push through German forces, they wanted to free Europe of German rule and stop Hitler. Hitler's goal during World War II was essentially to capture all of Europe and he needed to be stopped. Germany did not know where the Allies would be attacking from, so their confusion was high when the Allies started storming in. The Allies pushed deep within France, eventually pushing Germany back out.
Europe would no longer be controlled by Nazi Germany, the Allies now had a lead in Europe. Less than a year after the Invasion of Normandy happened, Germany surrendered.