I knew Hitler was a back stabber but.

[Anomalocaris]

It cost them too much materiel to get close and by then General Zhukov was sent to take command and later a whole shitload of Russian reinforcements arrived from the far east.  And then, towards the latter part of October, the weather began to turn.

Zhukov was in command of the Siberian units that were freed up when Sorge informed Stalin that the Japanese were opting for the "Southern strategy" rather than attacking eastern Russia. So him taking charge of the defense of Moscow and the (IRCC) 30 divisions of fresh troops was the same strategic move. He was one shrewd commander. 

I heard a Russian say that "both sides had the same weather!" True, but the Germans didn't know to mix fuel in with their crankcase oil in the winter to make it usable. And the Germans didn't have winter uniforms to any useful extent.

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He had no  choice. He needed the oil.

Stalin was providing him with oil and other strategic resources, including food, in the hope of avoiding an invasion. The German army also imported oil from Roumania. They commandeered, as I recall, 245 of the 258 river tankers in service at the time.

It helped that far eastern army, being furthest from Moscow,  was the least affected by stalin’s Purges, so retained the cadre of efficient professional officers and NCOs from before the purge.  Zhukov was familiar with the Soviet far eastern army, having commanded it in 1939 during the large scale border conflict with japan.

Regarding Stalin supplying Germany with oil and raw material, that was true.  But the reverse side of the bargain was Germany had to provide Russia with heavy industrial equipment and armament to help modernize Soviet defense industry and rearm.   Although Soviet Union assiduously provided Germany with all the raw material in the vain hope of avoiding a premature war with Germany Russia was not yet prepared to win, and Germany was tardy in delivering much of the promised war material because Hitler knew he would attack and these might be used against him, Germany still delivered some considerable armament supplies to Stalin in order to keep the secret agreement with Russia going until Germany was prepared to attack.  These includes blue prints for current german battleships (delivered but the Soviets were not impressed by them), german made heavy gun turrets for new Soviet battleships (actually manufactured but not delivered), new german built heavy cruisers for the Soviet Navy(actually delivered), blue prints for the latest german tank (delivered but the Soviets laughed at them because they were considerably inferior to latest Soviet designs), latest german artillery fire control equipment (delivered and which the Soviets appreciated).

Also, although Germany didn’t know the real scale of Soviet rearmament, they suspected the Soviets were gaining military potential faster than Germany and were preparing to attack in 1942 or 1943.   So Germany was concerned with Russia suddenly cutting the supply of raw material off, or mounting an attack against Romanian oil fields.  

Just like during the First World War, during the Second World War Germany also feared in the long run the relative strength between Germany and Russia will inexorably tilt in favor of Russia because of Russian natural resources and manpower, and having so much unfulfilled industrial potential that are being realized.  So as just before the First World War, during the second Germany felt the clock was ticking because the longer Germany waits to fight Russia, the more the relative superiority of Germany will fade and the stronger Russia will become relative to Germany.

At the same time as having grand strategic vision clouded by worries about Russian potential in the not too distant future, Germany also underestimated current Russian strength and resilience. it is tempting to use the napoleonic invasion of Russia as the template for determining how any attack on Russia will develop.    But that is somewhat in hind sight and selective in reading historic precedents.    In 1941, the most recent example of how war with Russia will fare was the 1914-1917 war on the eastern front, not the napoleonic invasion of 1812.   During that 1914-1917 war the Germans thrashed the Russians repeatedly, successfully invaded and seized large parts of European Russia, Russia proved unable to bear the strain, eventually suffered internal revolts and completely folded.  That war was settled in 1917 with Russia essentially giving up all of its European empire, including much of its population, and most of its industrial and agriculture regions to Germany.   Hitler had expected something like this will play out in 1941 as well.   He thought that, due to all the purges and all the brutalities, the communist government would be even more vulnerable to internal revolt than the czarist regime.  He was totally blind sided by how resilient the communist regime proved to be.

I think there is a important historic lesson here, especially in the era of angst that led to trump. Great powers rise and fall. Relative powers between different countries fluctuate. This can happen peacefully, with long standing powers, realizing the decline in its own relative strength, peacefully accommodate the rise of new and upcoming powers to ensure Long established institutions survive the transition, and the world remains peaceful.

But the danger of cataclysmic conflict is heightened if the long standing power indulges in exaggerated confidence in its present superiority, but suffer from morbid fear of future potential of up and coming powers. Then it become tempted to use its own current strength to trash institutions that has protected security and prosperity during the period of its own dominance in order to act to forestall the natural rise of up and coming powers.