KabulEvery morning, on Kandahar Air Field, the British, US, Canadian and Dutch troops like to start the day with a cappuccino from Green Beans, the US army’s answer to Starbucks. But a few weeks ago the soldiers had a nasty shock: a sign on the Green Beans door saying there would be no frothy coffee for the lads because of a ‘supply problem’ in Pakistan.War is hell, isn’t it? But the sign wasn’t just bad news for coffee-loving squaddies, it also revealed the Achilles’ heel for the entire international mission in Afghanistan: Nato’s supply roots, which are being steadily throttled by the Taleban.Politicians and generals can discuss strategy until they’re blue in the face, but absolutely nothing can be achieved if the supply lines collapse.