Talking About Military History: Why did Nazi Germany concentrate her armed forces on the Eastern Front against the Soviet Union in World War II?

Why did Nazi Germany concentrate her armed forces on the Eastern Front against the Soviet Union in World War II?

Aside from the fact that to the Nazis the Soviet Union was the principal enemy?

There were several reasons, really.

First, you must remember that by Adolf Hitler’s calculations, Great Britain was on the ropes and unable to reverse her defeat in Western Europe a year earlier. Yes, the Royal Air Force had defeated Germany’s Luftwaffe in the Battle of Britain and the Royal Navy was still a force to be contended with. But with Britain’s army scattered hither and yon in North Africa, India, and its Imperial holdings everywhere, it would take years for Churchill to field a land force strong enough to open a Second Front in the West. (Hitler was a land-bound “strategist” and failed to recognize that if he lost the air war and the Battle of the Atlantic, his Reich was doomed.)
Second, Hitler was counting on continued American neutrality (even though by June 22, 1941 this hope was becoming less realistic). He believed (with good reason) that the sentiment for continued isolationism was still strong in the United States. He also calculated that Japan’s moves in Southeast Asia would draw American attention away from Europe. He had no idea that Japan’s navy was preparing for the Pearl Harbor raid and the various invasions that were scheduled for later that year, but if he had known, he would have worried less about American involvement in World War II.
So basically, the Fuhrer decided to gamble with the destiny of his adopted homeland and concentrated most of the Wehrmacht against the Soviet Union. For Operation Barbarossa (the invasion of the Soviet Union), Germany fielded 3.8 million soldiers, 3,350 tanks, 2,700 aircraft, and 7,200 artillery pieces. These were organized into three Army Groups (North, Center, and South). In all, these forces consisted of 153 divisions, along with additional divisions provided by Romania, Italy, and Hungary.
Now, if you look at how big the Soviet Union is on any map that depicts its area on June 22, 1941, you will understand why the Third Reich concentrated much of its forces on the Eastern Front. The territories Hitler coveted were huge! And although he never planned on going beyond the Ural Mountains and on to Siberia, his stop-line that ran from Archangel to Astrakhan (the famous A-A Line) would have made his Greater German Reich, well, ginormous.
Hitler, of course, was not a total idiot. He still had large armies in Germany and the occupied countries in the West and Balkans. Even though there were less divisions in the West after Barbarossa was launched, they were still formidable enough to deter an Allied invasion of France until June of 1944.
And, yes, he realized that if the campaign in Russia bogged down and became a war of attrition, then the prospects of victory would dim. But Herr Hitler (luckily for the world) bet that his armies would crush the Red Army before the weather turned bad in October. (His arrogance is reflected in this quote: “We have only to kick in the door and the whole rotten structure will collapse.”)