War is used metaphorically in Act 3, Scene 3 when Othello becomes convinced that Desdemona is cheating on him:
. . .Ho, now forever
Farewell the tranquil mind! Farewell content!
Farewell the plumed troop and the big wars
That make ambition virtue! Oh farewell,
Farewell the neighing steed and the shrill trump
The spirit-stirring drum, the ear-piercing fife,
The royal banner, and all quality,
Pride, pomp, and circumstance of glorious war!
The quotation shows that once Othello believes he has lost Desdemona, he feels that everything that has given his life meaning is also gone:
Othello's occupation's gone!
We see that Othello is first and foremost a soldier, and many of his decisions regarding Desdemona are based on that background.
One great place to start is in Act I, scene iii, where Othello is discussing the current issue with the men of the city, if you will. He talks at length about the experiences he had, how his very person has been shaped by war, and how it also led to Desdemona falling in love with him.
There are a number of different angles from which you can approach this particular bit of text about war. The other places you might look are the portions of the play where they discuss the destruction of the Turkish fleet and the changes it will make for them, or the mayor of Cyprus talking about how they ought not to act like such ruffians in a "warlike" city.