When the self-styled Islamic State movement took control of Ramadi, capital of Iraq's Anbar province, it was another humiliation for the Baghdad government and another discomforting development for the United States which has bombed IS, but failed to neutralise the jihadi threat. Stephen Sackur talks to Emma Sky, a British woman who was a senior advisor to the US military in Iraq until 2010. Where do the roots of the current mess lie, and what should America and the West be doing now?