Most dog behavior problems arise out of an owner's misunderstanding of the proper role of the pack leader. (mokangreyhounds.org)
Due to their German Shepherd relatives (who, being the herders of the «pack», therefore quickly assume the role of pack leader), these dogs tend to exhibit pronounced leadership qualities and a desire to dominate. (animalso.com)
They would also interpret any attempt to take them as a challenge for the role of pack leader, and so would correct this using aggression if necessary. (theveterinaryexpert.com)