I think a case can be made for D-Day being the moment where the German loss became only a matter of time. At this precise instant, the war for the Germans became a two front affair, with the Russians in the Eastern theatre and the Americans and British on the Western side. Hitler and the Nazis had to fight two fronts, with equal magnitude and intensity. There was little way that Germany could possess the sustainable and replenish-able resources to fight both for an extended period of time. The Allied invasion of the beaches at Normandy also constituted the first time that Hitler was repelled from advance, and like all of those who bank of the air of invincibility, the first time that there is exposure of weakness is a significant instant, a confirmation that defeat is not that far off from being recognized.
The significance of this day is that it was the day on which the Allied forces invaded Normandy, France in World War II. The overall commander of this invasion force was Gen. Dwight D. Eisenhower, who later became president of the US.
Earlier in the war, the Germans had conquered essentially all of Western Europe. If the Allies were going to defeat Germany in this war, they were going to need to invade the mainland and, eventually, invade Germany itself.
The D-Day landings in Normandy were the first step of that invasion. The fact that the landings succeeded allowed the Allies to eventually push all the way into Germany and end the war in Europe.
D-Day refers to the landing of Allied forces on the Normandy beach in Northern France On June 6, 1944. In this operation about 2,700 ships carrying landing craft and 176,000 soldiers crossed the channel and stormed ashore on a 100-kilometre front in the largest seaborne invasion in history. The D-Day had a major impact on final invasion of Germany and bringing World War II an earlier close.
Success of this operation enabled Allies to build an artificial harbour for unloading more troops and supplies, and install a pipeline to carry fuel across the channel. Using these facilities about a million Allied troops had reached France by end of June, 1944. This paved way for liberation of France and invasion of Germany from the eastern side.