[Stephen Roach is among the most acute analysts of the risks inherent in the chronic US balance of payments deficit and low savings rates. Here he steps up his warning of the dangers of a meltdown of the global economy by a close examination of the vulnerability of the US and Chinese economies to a slowdown in US consumption related to oil and other factors. Japan nowhere figures in his simple story of forces driving the global economy, the implications for Japan and Asia are no less stark than those for China and the US. Japan Focus.]