How did blizzard entertainment got the idea for wrath of the lich king

Wrath of the Lich King wasnt just thought up as a sequal to the original and Burning Crusade. Wrath has been part of the story for over 10 years now. They only split the game in three because there was so much to develop. Anyway, everyone knows that World of Warcraft stems from mostly the ideas in the Lord of the Rings books. The races and some classes are exactly the same for one thing; orcs, elves, dwarfs, wizards and goblins. If you know anything about Lord of the Rings you can just look at the Lich King himself.