Going back to ‘Understanding Iran’s Motivations in Iraq - The Cost Calculus of External Support’ I would argue that the rhetoric from the current US regime is backing Iran into a corner and their best defence – to prevent being the next casualty of the US military – is to bog down US forces in Iraq and Afghanistan. Would it not then be a better option to engage them diplomatically and so cut off the insurgents support. That is certainly the message I took from the article. As to the Iranians being able to interrupt oil supplies true but also true for the US navy and others but as an oil exporter I can not see why anyone would think they would want to do such a thing – unless as a means of striking back after aggression on the part of the US. At present all the belligerent noise is from the US side, Iran has no interest in a war they are going to come out worst from.