Matt, Satan isn't actually a deity. It was a metaphor for the influence we allow Satan to have over us in this world. The Earth is the Lord's creation and God is King of the universe. You also can't "sell your soul" because all souls belong to God and will be called to judgement before Him one day. So, there is no real cosmic war going on. No creature can go to war with the infinite Creator, that's absurd. It is only by His mercy that He allows any of us to exist in the first place. There's only souls striving closer to God and souls falling further away from Him. Demons, like hellbound people, are in the latter category. Misery loves company in their case. They have no power and don't rule anything. They are good at illusions, though.