Okay let's see. If the Ark was still being chased 50 years ago and crashed on the moon isn't it possible that the Dread's thought they still needed to destroy Sentinel. Being that they were asleep all that time in stasie. Oh and why did Sentinel need protection from the Dread's. I mean seriously think about it we all seen how well he can fight, he could've destroyed them like 1,2 and 3.