Pyongyang last night conducted its first test of a hydrogen (thermonuclear) bomb. The device was ten times more powerful than any of those detonated in North Korea’s five earlier atomic (fission) nuclear tests, signifying yet another surprise breakthrough in the regime's nuclear program.

This is the first nuclear test during President Trump’s tenure, and the world will be watching to see how he responds. One thing is certain: this test will further roil the already unsettled dynamics in northeast Asia.

Technological Breakthrough

Seismic readings showed a magnitude 6.3 man-made explosion near North Korea’s known nuclear test site. According to preliminary expert analysis, that indicates an explosive yield of up to hundred kilotons. The previous high test yield was approximately sixteen to twenty kilotons—the approximate size of the Hiroshima and Nagasaki bombs.

Earlier this weekend, North Korean media showed Kim Jong-un inspecting a new warhead design, which differed from the “disco ball” warhead revealed last year. Pyongyang claimed it was an “H-bomb, the explosive power of which is adjustable from tens of kiloton to hundreds of kiloton [and] is a multifunctional thermonuclear nuke with great destructive power.” The graphic of the warhead shown to Kim was labeled as a hydrogen bomb for North Korea’s Hwasong-14 ICBM and is consistent with a thermonuclear (fission-fusion) warhead similar to U.S. warhead designs. The North Korean report also indicated Kim “watched an H-bomb loaded into a new ICBM.” North Korea’s last nuclear test was September 9, 2016 (North Korean Founding Day), and many experts had expected the next nuclear test on that day. Pyongyang may instead do another ICBM test on that day. The regime’s recent launch of a missile over Japan—its first since 2009—sets the stage for an ICBM flight over Japan.

Pyongyang claimed that its January 2016 nuclear test was of a hydrogen bomb, but this was dismissed by experts as being beyond the regime’s technical capability. It was presumed that North Korea might have instead achieved a boosted fission warhead in which hydrogen or tritium gas is inserted into an atomic bomb to boost its explosive yield.

As such, Saturday’s hydrogen bomb test surprised most experts. There has been a decades-long trend of dismissing or downplaying North Korea’s growing nuclear and missile capabilities. During the 1990s, some experts didn’t think Pyongyang had acquired fissile material for a plutonium-based atomic weapon. The George W. Bush administration was ridiculed for its insistence that North Korea was pursuing a parallel uranium weapons program, until the evidence for it became irrefutable. Initial reports that Israel had in September 2007 bombed a Syrian nuclear reactor built with North Korean assistance were also dismissed by some experts.

During the past two years, Pyongyang has achieved breakthrough successes in all of its missile programs, most notably in developing a submarine-launched ballistic missile, two different intermediate-range missiles capable of threatening U.S. bases in Guam and an ICBM that can reach most of the continental United States.

Test for Trump

President Trump now faces yet another challenge from North Korea. Earlier in the year, Trump vowed that North Korea's promised ICBM test “wouldn't happen,” but Pyongyang successfully conducted two ICBM tests in July. Later Trump threatened “fire and fury and frankly power the likes of which this world has never seen before” if Pyongyang made “any more threats to the United States,” which the regime promptly did.

Statements by Trump and senior administration officials suggested Washington was contemplating a preventative military strike on North Korea to keep it from completing development of an ICBM that could target with continental United States with a nuclear weapon. Leaked intelligence community assessments indicate Pyongyang may have already achieved that goal. However, subsequent statements by the secretary of state, secretary of defense and the CIA director downplayed the likelihood of an imminent U.S. attack.

Nervous U.S. Allies

South Korea and Japan have long harbored concurrent contradictory fears of U.S. abandonment and entanglement in a conflict. These concerns have grown in recent years due to declining U.S. military capabilities brought on by budget cuts, President Obama’s unfulfilled red-line threats, and Trump’s comments criticizing or questioning U.S. alliances. However, North Korea’s unrelenting threats and progress on missile programs have affirmed to Tokyo and Seoul the importance of their alliances with the United States.

Japan was unnerved by the latest North Korean missile overflight. Previous instances led Tokyo to deploy and then accelerate its ballistic missile defense programs. Japan has since deployed a robust missile defense program. And it may accelerate its recent decision to deploy Aegis Ashore to augment its existing Patriot and SM-3 systems.

North Korea’s test could also spur ongoing Japanese discussion for greater offensive military capabilities and authority for preemptive attack, previously taboo topics under Japan's post-war pacifist constitution. Though these would be logical steps in Japan’s slowly evolving security role, even the contemplation of such moves generates intense reaction by South Korea, which still deeply resents Japan’s occupation during the twentieth century.

Meanwhile, South Korean President Moon Jae-in has moved far from his liberal background. He now advocates a much tougher policy toward North Korea than many of us had expected. Moon has been driven to the political center by North Korea’s provocative behavior, its rejection of Moon’s repeated efforts at inter-Korean engagement, and domestic polls that show the highest support in history for the alliance with the United States.

Moon has reversed his previous policy stances and now declares his support for “maximum pressure” on North Korea, deployment of THAAD missile defense, and not reopening the Kaesong economic venture with Pyongyang. Moon, however, was unnerved by earlier perceptions that the United States was moving toward an attack on North Korea and claimed that Washington agreed to requiring prior South Korean approval before initiating a military strike. Reports that the Trump administration was going to withdraw from the bilateral KORUS free-trade agreement as well as its stronger criticism of South Korea than China for their policies toward North Korea were not well-received in South Korea.

Another Decision Point for China

Beijing again faces a decision as to whether it will continue supporting its troublesome ally or more fully enforce required UN sanctions and agree to even more stringent measures such as an oil embargo. But China has often fulfilled Yogi Berra’s advice of “when you come to a fork in the road, take it” by continually deferring on what seems to be an unavoidable inflection point.

While China has allowed incrementally better UN resolutions after major North Korean provocations, it has always insisted on weaker text than requested by the United States and has a long history of enforcing required sanctions only weakly and intermittently.

The Troubled Path Ahead

While North Korea’s hydrogen bomb test was a significant and dramatic technological “game-changer,” the United States still faces the same constraints on military actions as it did before. Any attack on North Korea risks triggering a massive North Korean response against South Korea and Japan and U.S. forces and citizens there.

A premature return to negotiations would be ineffectual as long as Pyongyang continues to reject the possibility of it abandoning its nuclear arsenal and production capabilities. Numerous attempts at dialogue, negotiations, and agreements have all failed.

The most prudent policy remains augmenting pressure on North Korea via a comprehensive, integrated strategy utilizing all instruments of national power. This would include greater enforcement of UN resolutions and U.S. law through sanctions and targeted financial measures as well as enhanced information operations against the regime, greater advocacy for human rights, and ensuring sufficient defenses for the United States and its allies, particularly ballistic missile defense.

Such a strategy achieves near-term objectives of responding to North Korea's serial violation of UN resolutions and U.S. and international law and providing incentives for Pyongyang to return to the negotiating table.

Rather than sudden regime change through kinetic military action as some advocate, change is more likely to come from within. But creating the conditions for such internal change requires rigorous and enduring support from the outside. External pressure can augment internal pressure against the regime, undermining the foundations of the regime and enabling the North Korean people to eventually bring about the downfall of the Kim regime.