It's an old question which still has no satisfactory answer: In Othello, what do you think Iago's motivation is? Is Othello one of the "problem plays" because Iago's motivation is not clearly described?
Of course, the simple answer is that Iago is enraged about not having been chosen as Othello's lieutenant, as he speaks of in the very first scene of the play. But is this enough of a motivation to destroy Othello, and Desdemona, and Cassio, and his own friend Roderigo?
My own belief is that the key – or at least an important clue – to Iago's motivation is in his scoffing attitude to Michael Cassio, of whom he says that he "never set a squadron in the field,
/ Nor the division of a battle knows
/ More than a spinster."
I think that Iago's only desire is to fight wars alongside the greatest warlord around, namely Othello. And I think that Iago believes that Othello will be incapable of being an effective warlord when he is in love, and, like Cassio, "damn'd in a fair wife".
As I see it, the conflict between war and love is a theme that three of Shakespeare's plays from this approximate point in time revolve around: Troilus and Cressida, Antony and Cleopatra, and Othello. All are about the emergence of the ideas and conventions of courtly love, and how these cannot thrive in a society so far obsessed with, or dependent on, warfare. In order for courtly love to gain ground, society must change, or love must die.
What do you think?