We all know how the early German Blitzkrieg campaigns wiped out the enemy's armies in a matter of weeks... First Poland, then the Low Countries, France, and making England retreat back to the island while leaving all their heavy materiel. The Western Allies had more troops, better tanks and more numbers of tanks, but a lack of preparation, bad tactics, a defensive attitude, and not using their air forces in any affective matter killed their campaign and allowed the offensive minded Germans to sweep in and take them out in almost record time. My question is, if Germany stormed into France but faced the Allies of around the time of D-Day (summer 1944), with the Americans, their massive materiel, air power, and troop numbers, and a planned joint-Allied effective strategy, would the Germans have had such an easy victory, if at all? I think it could have turned halted the Germans and eventually push them back. There could have been a WWI-style stalemate for a little while, but eventually the Allies with their massive materiel and reserves advantage pushed them back and stopped the Blitzkrieg.