The horrific images surrounding the gruesome execution of the US journalist Jim Foley are dominating the headlines. The Islamist group had several reasons for doing what they did, and when they did it.
It reinforces the Islamic State's reputation as the baddest Islamists of them all, a useful tool when you're looking to knock off your Islamist competitors in Syria. It also shows the US that there are costs associated with its air campaign, and the warning that there is another hostage at their mercy reinforces that warning; the English language audio track was designed for the target audience.
I don't however necessarily agree that one of the aims is to goad the West into becoming more deeply involved in Iraq. The Islamic State is as aware as anyone that neither the President nor the American people are inclined to do it, and there are many more ways to skin the Islamist cat than simply put combat troops into Iraq.
But these are relatively minor aims given the shock value that the vision was intended to produce.
People already know that the Islamic State is cruel and heartless, and they know the US isn't going to stop their air attacks just because Islamic State kills a hostage. Rather, I think the main point of the exercise was to do with the timing of the release. Islamic State had just suffered a couple of battleground reverses, having been rebuffed from Mount Sinjar and more importantly losing control over Mosul Dam, an important infrastructure prize for a putative caliphate. If you want people to stay with you, join you or submit to you, it's necessary to project an image of control and martial success. Images of destroyed Islamic State vehicles and equipment and triumphant Kurdish and Iraqi soldiers celebrating over ground you've just lost isn't good for business. In the space of a few hours though, this negative imagery was swept away by an execution video; people may have heard about Mosul Dam but they aren't reminded of it because those images are no longer displayed.
The Islamic State is very good at manipulating the social and news media space. And if it takes the beheading of someone to counter images of battlefield setbacks, then so be it. Such is the calculus of Islamic State's media department.