What would have happened if the Germans did not invade USSR, and if they have continued to focus on the west front with British? Bulk of German military forces and economy productivity were used to invade USSR. Over 3~4 million soldiers were fighting on the east front. Most of them were killed eventually by the Russians. When Normandy landing took place, there were fewer than half a million German forces in entire western Europe. (One source said there were only 400,000 of them in western Europe). If the Germans had continued to engaging the British in a bombing and submarine warfare with 100% of their military and economy powers, do you think British can hold off the Germans forever? Without engaging the USSR, Germans would have had much more materials and productivity to build planes and ships instead of tanks. The Germans could also have send reinforcement to Rommel in North Africa, sending him more troops and tanks. He wasn't getting any supply and replacement tanks for each of his loss later in that campaign. Without diverting most of their forces to the east, the Germans could have had enough planes in North Africa for Rommel too, they did have air superiority there earlier on until the Americans helped the British. If the Germans capture the oil fields there, they would have had unlimited fuel for the war too.