The exchange of artillery fire between the two Koreas, which follows revelations of 2,000 North Korean centrifuges producing uranium for a new reactor, constitutes a direct challenge to US president Barack Obama’s Asia policy. The latest gust of militarism and aggression from Pyongyang also demonstrates the fragility of the current system of power relationships throughout this critical region.

Mr Obama and Hillary Clinton, his secretary of state, in repeated trips have been at pains to declare that America is now focusing on east Asia, after the distractions of Afghanistan and Iraq. But China, in declaring the South China Sea a “core interest”, and now the actions of North Korea are challenging the US for primacy. A dominant US navy and air force will in coming years be challenged here by the rise of China’s own air and sea battle architecture.

North Korea’s aggression thus threatens not only South Korea but Japan, too. Its leadership is as much national-fascist as communist, and has manifested deep hostility to the Japanese, who occupied the Korean Peninsula from 1910 to 1945. In short, Japan is getting real-life experience of what maritime Asia would be like without unipolar America power.