The departure of General Stanley McChrystal as commander of the US and Nato mission in Afghanistan must usher in a review of what is a failing military strategy. At the same time, President Barack Obama's officials must demonstrate greater unity in dealing with America's allies and developing its approach. The appointment of General David Petraeus comes at a critical moment – when the crisis in Afghanistan is affecting the west's ability to project a comprehensive united foreign policy stance.

Much has been made of President Hamid Karzai's erratic and self-serving style of ruling, especially given last year's rigged presidential election and the corruption and poor governance of which he is often accused.

What is less well known is the dysfunctional nature of Mr Obama's team. Since they were appointed, the senior officials who decide US policy in the region have been at loggerheads. The White House has failed to consult Richard Holbrooke, the state department's special representative to the region. In Kabul, Gen McChrystal and retired General Karl Eikenberry, the US ambassador, have at times barely been on speaking terms. In turn, Gen Eikenberry and Ann Patterson, the US ambassador to Pakistan, have had sharp differences with Mr Holbrooke.