Why does Iago hate Othello so much?

This play confused me in the beginning. Sparknotes.com says:"Iago says he hates Othello, who recently passed him over for the position of lieutenant in favor of the inexperienced soldier Michael Cassio." I feel like there's a lot more to it than that.

This question is on my study guide for a long essay question on my final on Friday so I was wondering if you all could help me prepare in case I need to answer it. Thank you! More.

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.