It's being described as the worst humanitarian crisis on the planet. After decades of war, eight million people are now facing starvation in Afghanistan and a million children could die. Reporter John Simpson goes back to explore the shocking unravelling of a country he's been reporting on for more than 40 years. The Taliban takeover and sanctions imposed by the West have contributed to economic collapse. There's food in the markets, but families are being driven to edge because they simply don't have the money to buy it