Complex sentence: The magnitude of the defeat was so great that the mechanized corps parent headquarters of the tank divisions were either inactivated or destroyed by July 1941, with most of the tank divisions facing the Germans enduring a similar fate by the end of 1941.
Split into simpler sentences: The magnitude of the defeat was so great that the mechanized corps parent headquarters of the tank divisions were either inactivated or destroyed by July 1941. Most of the tank divisions facing the Germans had met a similar fate by the end of 1941.