North Korea today announced the successful detonation of its first thermonuclear bomb after sensors in South Korea identified a seismic event registering 5.1 on the Richter scale in the Hermit Kingdom’s northeast—a region where underground nuclear tests have been carried out before. Calling the test a “complete success,” an announcer on Pyongyang’s state-run TV channel described the weapon as a “self-defensive measure” against “threats and blackmail by the United States and to guarantee the security of the Korean Peninsula.”The United States officials, for their part, said they could not confirm North Korea’s claims at this time, but several independent experts expressed doubts that Pyongyang had managed to pull off a full-bore H-bomb. Rather, it was far more likely that North had managed to develop a boosted fission bomb, a traditional nuke that incorporates a small amount of radioactive hydrogen in its core to increase the damage it can do, but that falls short of a full-on thermonuclear device.The biggest loser in all of this, however, appears to be China, and the biggest winners are Japan’s Shinzo Abe and South Korea’s conservative government. North Korea’s test will strengthen public support in Japan and South Korea for defense buildup A) because nukes are scary, and B) because it demonstrates that China, which has far more influence in Pyongyang than anybody else, isn’t willing or able to control its client. If Beijing isn’t willing, that suggests hostility and encourages Japanese rearmament. If Beijing isn’t able, that demonstrates weakness, making the Japanese and South Koreans think they have to defend themselves against threats from North Korea, Chinese protests to militarization be darned. The detonation also makes the comfort women deal more likely to stick; a nuclear threat is a pretty strong incentive for traditionally-hesitant allies like Japan and South Korea to hug tighter.