If they didn’t decide to attack Russia when England was already weak, they could have focused their entire accumulated forces, supported by the industry and weaponry of Poland, Czechoslovakia, France, Belgium, Greece, Ethiopia, and all the other territories to fight. They could have build a world class navy using those resources easily, or just fired artillery across the channel and bomb the RAF bases and military stores in Britain. But Hitler decided to focus on London, and attack Stalin. When the winter came, he didn’t have his men stop, retreat, or supplied with warm clothing, even when the oil in their tanks froze while they were driving.