I recommend that anyone interested in this issue read Adam Tooze's "Wages of Destruction". This book is on the economic aspects of the 3rd Riech, from the economic history before the 3rd Reich, to how it conducted the war. But the book also engages in other aspects of German conduct of the war, including tactical and strategic reasons for this and that.
Tooze's book is the best explanation of the entire war, and it is fairly recently written history too.
Tooze' begins with what life was like for young Germans growing up in the last quarter of the 20th century, including a popular series of books that mesmerized German youth on tales of the American West, the conflict between cowboys and indians and the conquest of the West. Hitler would have had a hard time growing up and not being familiar with this. The period from 1870 to 1914 was a period of unprecedented economic growth and transformation of Germany, to the point where it eclipsed the United Kingdom in total economic output, (but not per capita output) especially in Steel, Electronics and Chemicals. This engendered pride for the German youth of Hitler's time. Germany constituted a sterling example of Western Civilization in many spheres of life, save politics. But when Hitler and people of like minds thought about the future, and looked at maps on the globe, it became clear that to continue to be a world power, Germany would have to take on continental proportions like China, Russia, perhaps Canada, India or Australia, and most definitely that of the United States, which as the Cowboy an Indian books illustrated, was taken forceably from the primitive people in the Native American Indians by an advance civilization, which increasingly was populated by ethnic Germans immigrating from Germany - at a rate of over 200,000 a year in the last third of the 19th century. To Hitler, for Germany to be a world power, it would need to have continental proportions, like that America got from the West. To this Hitler proposed Germany doing to the area east of its frontiers, what America did west of its frontiers, taking that land from what Hitler, and what many other uber-German nationalist viewed as an inferior peoples, the Slavic peoples of Poland and the Soviet Union.
What was driving this was long term, strategic economic interests and needs for economic resources. Russia had these.
The economic resource calculation drove events and decisions as even the discussion that Hitler had with Mannerhiem demonstrates, although I'm not sure if that discussion was not forthrightly honest, but taylored to Finnish ears.
Germany's strategic situation was little different than the UKs. It was an over crowded nation, that had a diet heavy in animal fats, that was too small to produce enough food of the kind it liked to eat. Prior to WWI, Germany had some Iron Ore to feed its industry in Alsace Lorriane. After WWI, those territories were lost and so all Iron Ore consumed by Geman Industry required foreign exchange reserves gained through manufactured export, only now, saddled with heavy reparations payments, such foreign exchange reserves were dear, hiegtening the strategic considerations Hitler's mind was already attuned to. So like England, Germany had an over crowded land, that had to export manufactured goods to pay for raw material imports. Unlike England, now Germany lacked a world class navy to ensure the steady flow of raw materials and food stuffs - meaning Germany was subject to interuptions to their economy, among others, by a British navy.
Much is made of Chamberlains concessions to Hitler at Munich. Tooze addresses some of this too. Prior to WWI, Europe was the center of the world, and the center of world power, and global economics. After WWI, the British and French were in massive debt to the United States while Germany's economy was highly dependent upon American loans. It was feared by both the British, Chamberlain specifically, and the French that another outbreak of a general war in Europe would have no other effect other than to make the European powers more fully pushed into 2nd rank powers dependent upon the flanking powers: the United States or Soviet Union/Russia. Chamberlain assumed that Hitler realized this too, and so at heart was not really interested in a new general war. Furthermore, Chamberlain fully believed that the Germans could once again be defeated by sound defence on land, and economic blockade that would bring Germany to its knees as what had happened in WWI. So to avoid a war that would render Britian a 2nd class power and satelite to the U.S., Chamberlain was prepared to sacrifice the Sudentenland as a way of throwing Hitler a bone and saving face. It was a crucial mistake. If Munich had not happened and Hitler had gone to a general war over the Sudentenland the German generals were ready to overthrow him. The outcome of Munich made that impossible. Shortly after Munich, Hitler cajoled the rump Czech state to request help in putting down an internal revolt, which gave Hitler legal pretext to send in troops, in effect conquering Czech without firing a shot. Stalin and the Russian saw the sell out of the Czech republic as firm evidence that the Western powers couldn't be trusted, so instead he chose to cut a deal with Hitler, the Nazi-Soviet pact. This pact was mostly economic, but it also divided up Poland which both powers saw as Repugnant. The Nazi-Soviet pact in a single stroke eliminated the threat any blockade would have on the Germany economy. Chamberlain's diplomacy was a total disaster.
Hitler's Germany, in Napoleon's parlance, occupied the central ground and proceeded to take on all surrounding powers in series, much the way Napoleon did in Italy and Germany during his day. He did this counter clock wise: First Poland, then Norway and Denmakr, then France and the Low countries, ideological friendly with Franco in Spain in the Southwest, alliance with Italy to his south, then invasion and attack of the Balkans to his Southeast. That brought him back to the issue of Russia.
Several things are added to Hitler's calculation. A sheer hatred of Communism and a belief it was decadent. The recent, massive purge of the Soviet officer corp. The demonstrated failure of effectiveness in the Soviet attack on Finland. Russia's poor performance during WWI, when it had what he would have thought of as a superior political system. Hitler's highest risk had been diplomatic move on the Sudentenland and Czech, Poland (because a more aggressive Western powers could easily roll into the Rhineland while the bulk of Germany's forces were in Poland), and then the attack in the West where the Germans faced superior numbers in men and material, even in tanks. What the Germans had going for them however was a superior battle doctrine, an excellent battle plan in the Manhiem plan, courtesy of the German general staff (and thanks to the original plan being exposed by a German plane accidentally landing in Belgium). All these other invasions, going into them, seemed like and probably were on the surface, higher risks. By the time Russia came along invading Russia seemed proportionately a much, much, much lower risks. Hitler had no idea that the Soviet people would react almost in unison to strive against him, this manifested in the miracle in the massive removal of Soviet industry to the Urals, nor could anyone know that the Russian's had a new tank, about to be produced in huge numbers that was superior to any that the Germans had. The reaction of the Russians was to fight and die in appauling conditions.
A side note is that, one possible reason Stalin refused to believe that the Germans would attack him in the run up to barbarossa, was that there had been no inflections in the price of wool in international commodities markets. You don't invade Russia without going out on world markets and purchase enormous quantities of wool for equiping your soldiers for Russian winters.
The reason Tooze gave for German declaration of war on the U.S. after Pearl Harbor, was because Hitler always believed that the U.S. would come in on the side of Britain sooner or later. Hitler had no antidote to the combined navies of Britain and the U.S., but Japan did have a substantial navy that could tie down one or even both. So Hitler continuously encouraged Japan to attack the U.S., and promised that Germany would declare war, as a sweetner, immediately after if Japan did. Japan did at Pearl Harbor, and Germany followed suit, as Hitler had promised.
One other side note is that, in the short run, instead of attacking Russia in 1941, a third of the resources used there, could have been applied to attacking Egypt, and a break through there, would have opened up the entire resources of the Middle East to Germany, most specifically, Oil. It would have required some accomodation with Turkey to best get the oil to Germany, but it would have rendered the entire Eastern Mediterranean to the Axis powers. This would have been nothing more than a continuation of the war with Britian. This is one of the big "ifs" of WWII.
German conquest of the Middle East would still have been a side show. Hitler's main strategic, long term plan was to take European and perhaps western Siberian Russia away from the Soviets, and Germanize it. And Russia was perceived as very weak at the time of the German invasion.
As for possibility of conquest: Russia was successfully conquered by the Mongols who controlled Russia for more than 200 years. The Poles had recently won a war over the Soviets in the early 1920s, extracting territory, which is why Stalin agreed to the division of Poland, to get back the land lost in 1920s. Finally, during WWI, Germany was signally successful on the Eastern front, but unsuccesful on the Western front. In WWII, it was just the reverse. Again, all of this made Russia look like a small risk. Too much reliance on hindsight? Perhaps.
Finally I dispute that Hitler insisted on the taking of Moscow. That was the goal of Guderian and the German Generals, but Hitler stalled the assault on Moscow and redirected Guderian south to form a pincer move behind the giant Soviet reserve armies in North Eastern Ukrain, in coordination with German armies of the South (Ukraine) moving north. This was successful, but it did delay the assault on Moscow -- which turned out to be just a smidgeon too far for them.
Production numbers Tooze assembles shows that Russia simply out produced Germany on most strategic weapons, and quite often in enormous numbers. That coupled to Soviet soldiers willingness to fight and die under impossible conditions, conditions that even the Germans shrank from, sealed Germany's fate in Russia.
Please note a few of the points here were not from Tooze's book, but by far most of them are. It's a good read, go out and get it. Economics explains much of the course of the war better than most other explanations.
