Complex sentence: Kyle was able to push Nekron back into his dimension by freeing the undead Lanterns from the demon lord's controls as not only they were his army; they were Nekron's anchors to the living universe as well.
Split into simpler sentences: Kyle was able to push Nekron back into his dimension by freeing the undead Lanterns from the demon lord's controls. Not only were they his army; they were Nekron's anchors to the living universe as well.