Complex sentence: Despite not having a defensive line of entrenchments, Allenby reviewed the threat of counterattack and his supply situation and decided a force large enough to attack into the Judean Hills and another separate force to operate on the maritime plain could be maintained far from base.
Split into simpler sentences: Despite not having established a defensive line of entrenchments, Allenby reviewed the threat of counterattack and his supply situation. He decided that a force large enough to attack into the Judean Hills, and another separate force to operate on the maritime plain, could be maintained at an extended distance from base.