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.

This is a terrible prospect. Alas, there are no good options for preventing it. Talking is always worthwhile, but North Korea is unlikely to give ground—and is untrustworthy if it says it will. A pre-emptive attack on North Korea’s nuclear facilities should be out of the question. The North’s existing weapons, including shorter-range missiles with fission warheads, would imperil the lives of millions of South Koreans and Japanese, as well as around 300,000 Americans who live in those countries. Chinese state media have debated whether China should squeeze North Korea’s oil imports. However, this would hurt ordinary North Koreans first, and China does not want to squeeze so hard that Mr Kim’s regime collapses.