The September 3 nuclear test opened a new chapter in North Korea's history of bellicosity. The powerful seismic tremor generated -- from 6.1 to 6.3 magnitude -- indicated that it probably was a hydrogen bomb at an early stage of development.

Early press reports ascribing a 100-kiloton yield probably underestimated the bomb's power. Later estimates ranged from 158 to 542 kilotons, with 300 kilotons being the most likely. That's the size of many bombs in the U.S. arsenal.

Frightful though North Korea's weapons may be, they are unlikely to achieve Kim Jong Un's strategic goal of decoupling the United States from its Asian allies. Recent opinion polls show Americans to be all the more determined to retaliate if North Korea were to attack Japan or South Korea. A strong deterrence posture, extended to allies, is the most well-practiced means of containing nuclear-armed adversaries.

This does not mean the world should accept a nuclear-armed status for North Korea. The goal must continue to be denuclearization. Achieving this goal becomes more fraught, however, with each advance in North Korea's program. Most experts conclude that North Korea will not voluntarily trade away its nuclear weapons for any degree of economic and diplomatic benefits.

U.S. policymakers believe pressure could force capitulation, and that China can be induced to use its leverage to this effect, for example, by shutting down Pyongyang's oil pipeline. Yet this is a regime that allowed up to two million of its people to starve in the mid-1990s. In any case, China will not apply the desired pressure unless it gets something tangible in return, such as withdrawal of the Terminal High Altitude Area Defense missile interceptors now being deployed in South Korea.

Most military strike options are not credible. Even a single cruise-missile attack against a missile on the launch pad would be seen by Kim as an opening salvo to an invasion. He would most likely respond with massive force in his own effort at pre-emption. North Koreans would lose the ensuing war but take maybe a million South Koreans with them, along with U.S. military personnel.

Many South Koreans believe the best response is to build leverage with North Korea and China by developing their own nuclear weapons or by reintroducing the U.S. tactical nuclear weapons that were withdrawn 26 years ago. But seeing how China responded to the THAAD deployment by restricting trade and tourism, it is unlikely Beijing would bow to coercive nuclear measures by Seoul.

Moreover, the U.S. has no interest in redeploying tactical nuclear weapons that take extra manpower to protect and offer no strategic capabilities that are not already in play via nuclear-armed submarines and nuclear-capable bombers.

Nuclear bases in South Korea would be a target for North Korean pre-emption and a flame for rekindling anti-Americanism. U.S. security guarantees would be jeopardized if Seoul broke its nonproliferation commitment. It would automatically trigger a cut-off of foreign fuel supply to South Korea's crucial nuclear energy industry and tarnish the nation's international standing. Japan, where the pro-nuclearization voices are smaller yet growing, would face similar downsides.

Not all military options are infeasible. Ballistic missile defenses are imperfect but can provide some protection, especially against intermediate-range systems that might target Japan. The U.S. and its allies might need to consider maritime interdiction of North Korean shipping as part of an effort to cut off Pyongyang's access to international trade. More attention may be given to cyber tools to disrupt North Korean missiles.

Meanwhile, concerned states must create communication channels to Pyongyang -- not to offer inducements but to reduce the risks of misperceptions that could lead to war.

(Mark Fitzpatrick is Executive Director of the International Institute for Strategic Studies (IISS) -- Americas, and a former senior official of the Department of State.)