Complex sentence: Most importantly, Hitler was unwilling to give up any ground that his soldiers had taken, resulting in a rigid defense that did not allow his forces the opportunity to maneuver to better counter the moves of their enemy or withdraw to shorten their frontage.
Split into simpler sentences: Most importantly, Hitler was unwilling to give up any ground that his soldiers had taken. This resulted in a rigid defense that did not allow his forces the opportunity to maneuver to better counter the moves of their enemy, or to withdraw to shorten their frontage.