Complex sentence: The Soviet reserves had been sent south, to defend against a German attack by the III Panzer Corps and with the loss of their reserves, any hope they may have had of dealing a major defeat to the SS Panzer Corps ended.
Split into simpler sentences: The Soviet reserves had been sent south to defend against a German attack by the III Panzer Corps. With the loss of their reserves, any hope they may have had of dealing a major defeat to the SS Panzer Corps ended.