Let's not forget about the opium.
I was going to say that.
After all if you start a war just for profit you should not ignore the money that can be made in drug business. Controlling worlds largest opium producer should give you a sizeable share of the drug market. (Or if this seems too obvious you could start burning down the fields in Afghanistan to take out your competition and then start producing opium in your own country.)
But that would be wrong. Just like starting a war for oil, diamonds, silk etc.