Their entire front against Russia was eventually reliant on their ability to drag heavy artillery and supplies through the dangerous mountain passes of the Carpathian mountains. An example of what they went through for their country: https://upload.wikimedia.org/wikipedia/commons/4/42/Wintersc...
Supply lines are the often unspoken critical pieces of the puzzles for any great war before mid-WW2. Poor logistical planning in their invasion of Russia was also was a major factor in why the Nazi's lost WW2 - which is where Germany really lost the war, the "war of the Atlantic" and later western front with the Americans was just the multi-year delayed wrapping up action where they had very little odds from the beginning.
This second book [2] has a great overview about why the Nazi's had actually lost the war by 1941 (and very obviously by 1942) due to poor logistical planning of Operation Barbarossa, largely due to the strategic planners overconfidence in the German superiority over Slavs after they swept the French/British out of Europe. The next 3yrs were just Hitler's delusions keeping it afloat.
[1] https://www.amazon.com/Collision-Empires-Eastern-General-Mil...
[2] https://www.amazon.com/Operation-Barbarossa-Germanys-Cambrid...
Remember the Nazi's invasion depended on their multiple tank groups making a very fast progress through this country, until they reached Moscow. It was not total war combat until much later.
Many of them were halted or destroyed when they faced a single inantry group backed by a KV-1. That was enough to cripple their invasion (among the other equivalent Russian tanks).
If you don't believe my account I highly recommend this book which is the best coverage of the eastern front, and questions much of the popular accounts of WW2 with some great research and plenty of citation:
https://www.amazon.com/Operation-Barbarossa-Germanys-Cambrid...