My thoughts after reading on German economy and preparations for war in 1941 :

Germany was in no way prepared for a long war as Barbarossa begun. Instead Hitler was sending men from the army to civil life and production figures were not boosted to help the front at all. So that is the biggest reason why Germany simply could not win the war if it went on for a longer time. Everybody else was producing everything for war at the highest possible speed and Hitler just acted like everything was already won. That was a big mistake. So even if figures in 1944 for production were good for Germany they were a long way behind the enemy´s total figures.

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