It's a device more powerful than any the country has tested before and the move threatens to undermine an already fragile security situation in the region. How will the latest move by Kim Jong Un, North Korea's young and unpredictable leader, play out?
The bottom line is that a hydrogen bomb, if that's what it is, is a much more powerful device than a more simple plutonium or uranium bomb, and that's worrying.
Moreover, every time they do a test they improve the quality of what they can do and one of their main goals has been to miniaturize a device
so they can put a warhead on a missile with a longer range.
We don't for sure that they've reached that point that but every test is a major step forward and the North Korean nuclear scientists will be assessing the lessons and figuring out the next step.
Can we independently verify North Korea's test claims?
The South Koreans and the Americans have ... technology that monitors the air for trace elements, radiation. There are things they can use but we may never know 100% and it may take a little time to figure it out.
We don't know how successful it was but if North Korea says it's a hydrogen bomb and you're making your calculations on how to respond, at this stage, there's no reason not to assume that it wasn't successfully done.
This is all moving in a direction that's got to be extremely worrying for everyone in the region.
How is China -- its long-term ally -- likely to react?
It's a real slap in the face to the Chinese and Beijing has got to be absolutely furious.
There was a period when the Chinese were really angry with the Koreans but some months ago there were signs of a clear shift in the Chinese approach. They sent a senior official, Liu Yunshan
, to a big military parade in October, standing right next to Kim Jong Un. It was all smiles.
We may have seen a precursor of this with the bizarre case of the all-girl band who canceled their China tour.
They came to Beijing just as Kim announced they had a hydrogen bomb capability.
Clearly, the North Koreans are not weak and vulnerable to Chinese pressure. Or they calculate that the Chinese are not going to do enough to make a difference and I think they are right.
President Xi Jinping has a huge amount on his plate. He has an anti-corruption campaign, a slowing economy, domestic discontent and he's got tensions brewing with many of China's neighbors and the United States.
In the end the Chinese calculus is that instability in North Korea is more dangerous than a North Korea with bombs.
Why does North Korea want a nuclear bomb?
I would say the last thing the North Korean regime is suicidal. They're not going to -- out of the blue -- drop a bomb on California. What this is designed to do is to send a message to everybody: Don't mess with us.
Equally, what they would like is recognition, legitimacy and some kind of peace treaty with the United States.
But they want it on their own terms and they've said to the U.S: We're willing to talk to you but we're not going to do it with preconditions.
The U.S. says the only basis for negotiations is to discuss how to get rid of the North's nuclear capability.
What action could the United States take?
From the U.S. point of view, what are the choices?
You can go to war with North Korea, which has its obvious drawbacks. You can try sanctions, which have to hurt the North Korean economy to some degree, but there's no evidence that it's produced a positive change in the way the regime behaves.
Even if you ratchet things up, it's not going to change the North's behavior. The regime doesn't care if people suffer.
What does that leave you with? Politics of outreach to North Korea under these circumstances in an election year are virtually impossible.
The odds are that the North will carry on and each time they do this, their nuclear capabilities grow. So while everyone else is focusing on ISIS, Saudi Arabia and Iran and Donald Trump, Kim Jong Un is gradually building up a nuclear arsenal.
The more he has, the more it might be tempting to sell that capability to bad actors. It's a very bad situation and unfortunately, I don't see any good outcomes.