I COULD cite endless sources & prattle on and on in academic prose, but the fact of the matter (and the historical reality) is twofold. The Nazis were stopped in their invasion of Russia by:
1) The tremendous will of the Russian people, who simply refused to give in. When they were surrounded (even entire cities), they still would not capitulate or surrender. If it was a siege mentality the Nazis desired, the Russians gave it to them. Of a surety, many died (and more suffered) -- but the delay (sometimes, tremendous) was enough to cost the invaders ultimate victory. In a military setting, oftentimes victory delayed is victory denied.
2) Secondly (and chief among the reasons), the Nazis were not only delayed -- they were divided. From a strategy standpoint, they simply took on too much of a task. Glance at the actual big map or blueprint of battle: In addition to the already-daunting fight moving westward across Europe, they now sought to conversely move across the Eastern front and invade an infinitely stubborn Russia. This might have worked well (or at least, differently) had the Nazi Army been twice the size. Military historians must admire their optimism, but in no way the logistical accuracy or finite correctness of such a tepidly silly invasion, of which the outcome was a foregone conclusion. The ONLY way such an ambitious invasion would have worked was, if the will of the Russian people had been weak and they readily waved their hankies out the window at first opportunity. In reality, the exact opposite occurred.
IN SHORT, the Russians delayed the inevitable outcome of the invasion, and the Nazis (most unwisely) divided themselves and their resources; this untimely combination of delay and division spelled defeat -- in any language.
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