Morgoth/Melkor could not be conqured by force of arms, and it was the vanity of the rebellious Noldor elves to think they could, Morgoth was only banished to a void beyond the world by the power of the Valar.
The lesson: Not by works is there salvation, but only by the grace of Jesus the Christ, our Lord.
You need to read the Silmarilion, the truth is there.