"On D-Day, the Allies landed around 156,000 troops in Normandy."
Source:
http://www.ddaymuseum.co.uk/d-day/d-day-and-the-battle-of-normandy-your-questions-answered#troops
That's a heck of a lot less than a million. And it turned the tide of the war.*
*I am in no way endorsing the nonsense that was the Star Wars prequels. This post is merely about the numbers of troops required to invade a continent and send it's oppressors running.
That figure doesn't seem to include the personnel manning all of the ships that ferried the troops over to Normandy, the pilots, air and ground crew of all the aircraft involved in Overlord, and don't forget all the personnel back in England overseeing the entire operation keeping track of the progress of the landings, making sure that supplies are ready to go over to Normandy, and making sure the troops' pay is being properly accounted for. All said and done that 156,000 probably at least doubles, if not triples when you factor in how many support personnel are required for every rifle toting grunt in the field. Not to mention that this was just one operation of the war, after we secured the beachheads in Normandy we sent follow on troops to continue the push, we didn't rely only the 156,000 that landed on Normandy on D-Day, many more troops continued to pour in after D-Day +1, 2, 3, and on.
In addition to the ground troops slogging it in the fields of France and on into Germany there were also countless numbers of personnel fighting in the skies over Europe, around a dozen men in heavy bomber with formations of dozens of bombers and then there's their fighter escorts. On the ground there's the ground crew that keeps all of those planes fueled, armed, and repaired; then there's people working the airfields themselves, working the control towers, guarding the airfields, cooking and feeding everybody, making sure they get paid on time, and then there's the medical staff to treat sick or injured personnel.
All of the above was just in Europe and the US alone ran 2 major air bases, one in England and one in Italy. You have duplicates of this in France and elsewhere that do the same thing for the ground units and all of this was duplicated over in the Pacific Theater and none of this factoring the Navy which accounts for a lot of people as well. So when you account for everything a million man army isn't really that impressive, especially when you're fighting a war that spans nearly an entire galaxy.