To deter North Korea, America and its allies must speak with one voice

ON SEPTEMBER 3rd North Korea tested what it claimed was a hydrogen bomb. Whether it was really that, or merely a boosted fission device, is unclear (see article). What is certain is that the bomb was hefty enough to cause big earth tremors in neighbouring China. Seismic data suggest the blast was around 120 kilotons—at least eight times more powerful than the North’s previous test a year ago. If converted into a warhead small enough to fit on its Hwasong-14 intercontinental ballistic missile, it could kill nearly everyone across a 15-square-kilometre area. Even if Kim Jong Un’s ruthless regime does not have a hydrogen bomb today, it will within a year or so probably have mastered a technology that has the potential for almost unlimited destruction.