If Hitler had invaded Russia 3 or 4 monthe earlier as the original plan...the Germans would have not been bogged down in the very harsh russian winter and may have destroyed the Red Army and the commies. But Hitler delayed the invasion to help the Italians finsh off the italians weak effort against Greece. I read that little tidbit in “The rise and fall off the third reich” A master (to a point) political manipulator and conniver but a very poor general. Many German generals felt the war was over as soon as it began.
A one-sided take of things to be sure but packed with telegrams that passed back and forth between himself, Roosevelt and Stalin. Stalin was clearly not happy at all that it took the West so long to open that Second Front (with D-Day). He considered our actions in North Africa, the Mediterranean and Italy of little consequence. He wanted that channel crossing and he wanted it now!