North Korea tested a nuclear device today that Kim Jong-un claims was a miniaturized hydrogen bomb, capable of being fitted to an ICBM.

But some experts doubt that claim, which raises questions why Kim would lie about the test.

What makes some experts skeptical is that the first measurements of the blast yield suggest they detonated either a high yield fission weapon or a very small, low yield fusion device. At an estimated 100 kilotons, the test was about 10 times more powerful than any previous nuclear test by North Korea. But successfully testing a hydrogen device carries with it engineering challenges that many believe is beyond the capability of the North to solve.

A thermonuclear device is triggered by a fission explosion, much like the bomb used to destroy Hiroshima. The heat from the detonation fuses hydrogen atoms which release enormous amount of energy. But miniaturizing such a device requires the capability of manufacturing a warhead  with engineering tolerances thought to be beyond the ability of the North to achieve - at least, according to South Korean intelligence.

But it's certainly possible that the North detonated a fusion bomb that would not be small enough to use as a weapon. The first US fusion bomb test - "Ivy Mike" in 1952 - was the size of a small house and exploded with a yield of more than 10 megatons, which was a thousand times more powerful than North Korea's test. 

It's impossible at this point to confirm a hydrogen bomb test. Further investigation, including identifying and measuring isotopes that will eventually make their way to the upper atmosphere is the only sure way to identify the type of nuclear explosion. Meanwhile, can the US afford not to act as if the North posseses the ability to create hydrogen warheads? We must proceed on the basis that what Kim says is true - which is part of his plan to use nuclear tests and missile tests to split the US from China and Russia and cause friction between the three allies in the region - South Korea, Japan, and the US.

Foreign Policy:

In addition to advancing its military capabilities, Pyongyang’s missile and nuclear tests have the diplomatic goal of driving wedges among the United States, its allies, and China. The Kim regime seeks to divide its neighbors to extract concessions, bust sanctions, and forestall increases in coordinated pressure. Yet if the United States strengthens trilateral cooperation with Japan and South Korea, it can counter Pyongyang’s threats and encourage China to force North Korea back to denuclearization talks.

Pyongyang’s ability to divide Washington and Tokyo depends on the Trump administration’s capacity to reassure Japan, and how proactive the Abe government appears on security policy. In the face of North Korea’s actions, Japanese could perceive the Trump administration as distracted by political issues ranging from Russia-gate to Charlottesville. Meanwhile, a U.S. leadership focused on alliance burden-sharing could interpret Japan’s growing need for extended deterrence as free-riding.

Yet even given this, Pyongyang’s odds of dividing Washington and Tokyo are slim. The U.S. government is very supportive of Japan; official attention and commitment are strong, despite domestic demands and a still understaffed administration. Moreover, the Abe government is keen to increase defense contributions and coordination with the United States.

North Korea’s provocations are more likely to complicate relations between Seoul and Tokyo. Security cooperation between South Korea and Japan has recently improved, including high-level dialogues, intelligence sharing, and anti-submarine and missile defense exercises. However, this progress remains tentative and under-advertised by the South Korean government to its own public.

Below the surface of relations between South Korea and Japan - and sometimes not so invisible - is the history between the two countries, especially the brutal Japanese occupation during World War II. But it's a given that the threat from North Korea has forced the South to try and put aside the history between the two countries. Kim's efforts to drive a wedge between Japan and South Korea will likely fail, as will his efforts to force a break between China and the US. 

The more Kim escalates, the closer he comes to seeing his regime destroyed.