Why Did Morgoth Take Radically Different Approaches to Men and Elves?

In my recent video on the Tale of Adanel (https://www.youtube.com/watch?v=tcOISb-59rw&pp=ygUTdGFsZSBvZiBhZGFuZWwgZmFsbA%3D%3D) I discussed how Morgoth seems to have taken a very different approach to dealing with Men as compared with Elves, but why would his strategy change?

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